The organization that has both received the Nobel Peace Prize and has been called the “gold standard” on climate change science has just issued its latest installment of its ongoing series of reports. The takeaway from the report is, “Oh crap, this is bad.”
On August 9, 2021, the Intergovernmental Panel on Climate Change (IPCC) issued its sixth report on the physical science aspects of climate change. I fear that when many people hear the words “climate change,” they hear “blah blah blah.” Or maybe they think, “not again.” Possibly they think, “fake news.” They should be thinking “this is awful. What do we do now?”
Think of the IPCC’s previous reports as thirty-years’ worth of wake-up calls regarding climate change. Let me come up with the right analogy about the current report. It’s like the doctor telling the patient who has smoked four packs of cigarettes a day and had a bad, bloody cough for years that he has stage-four lung cancer. Maybe it’s like ignoring the five “warning—bridge out” signs and then crashing through the barrier and realizing you are airborne. Get it?
The IPCC is made up of scientists from around the world who operate as an independent part of the United Nations’ World Meteorological Organization. Since 1990, it has issued five complete reports. In 2007, it really did win the Nobel Peace Prize (along with former Vice President Al Gore), “for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change.”
The IPCC’s current report is called Climate Change 2021: The Physical Science Basis (part of the sixth report to be issued by them). The multi-thousand page Physical Science Report was written by 200 scientists from different disciplines, drawn from countries around the globe. IPCC boiled down its full report into a 41-page Summary for Policymakers, which is detailed and informative, I suggest you start there.
If the IPCC follows the pattern of its previous reports, over the coming months it will issue reports on the following topics:
- The Physical Science Basis (the current report)
- Impacts, Adaptation and Vulnerability
- Mitigation of Climate Change
- Synthesis Report
Note: This article started as my notes about the Physical Science summary report. As a result, many sections are cut and pasted from the IPCC’s summary document for ease of reference. I didn’t put quotation marks around all of the quotes, instead I indented and italicized them. The summary and full report are written in dull, scientific jargon. I’ve tried to explain it in terms a layman could understand. Assume any snarky comments are mine. Also, I picked out what I wanted to highlight. If you do not care for my notes, that’s fine, write your own article.
Before jumping in, let me take a brief moment to explain the meaning of climate and how that is different from weather. According to the National Oceanographic and Atmospheric Administration (NOAA):
Weather is a specific event—like a rainstorm or hot day—that happens over a short period of time. Weather can be tracked within hours or days. Climate is the average weather conditions in a place over a long period of time (30 years or more). When scientists talk about climate, they’re often looking at averages of precipitation, temperature, humidity, sunshine, wind, and other measures of weather that occur over a long period in a particular place. In some instances, they might look at these averages over 30 years.
Thus, on an unusually cold day in July, when the talking head on radio says, “Whatever happened to global warming? Haha.” Remember, climate is looking at averages of weather events over lengthy time periods, not a day or even a season.
Dr. Michael Mann, the climate scientist from Penn State, says, “The basics of climate science are actually very simple and always have been. Carbon dioxide in the atmosphere traps more heat, we are adding more CO2 to the atmosphere. The rest is details.”
The IPCC discusses the details in their report.
IPCC’s Headlines
Following are some headlines from IPCC (yes, they came up with their own headlines).
A. The Current State Of The Climate
A.1 It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.
IPCC’s opening salvo is that we humans have warmed the atmosphere, ocean and land. This has resulted in “widespread and rapid” changes. They make this statement “unequivocally.”
Understand that the scientists used the unusual term “unequivocal.” Albert Einstein wrote a “theory of relativity.” Charles Darwin wrote a “theory of natural selection.” Even though they are theories, most scientists accept Einstein’s and Darwin’s theories. The IPCC’s scientists use the term “unequivocal.” See the difference?
More importantly, the IPCC scientists say that warming of the atmosphere, ocean and land has been caused (at least in part) by humans. In IPCC’s First Scientific Assessment in 1990, it was willing to say, with certainty, only that “human activities are substantially increasing the atmospheric concentrations of greenhouse gases” and “these increases will enhance the greenhouse effect, resulting on average in an additional warming of the Earth’s surface.” [1] In its latest report, the IPCC says, “It is unequivocal that human influence has warmed the atmosphere, ocean and land.”
This is presented as a finding of fact with high confidence. That means the hundreds of scientists who evaluated this agreed as a group that the finding was one in which they had high confidence. In thirty years, the IPCC has gone from making a statement that human activities are substantially increasing greenhouse gases which in turn is enhancing the greenhouse effect, to its unequivocal statement that human influence has warmed the atmosphere, ocean and land.
The IPCC’s meaning of confidence levels and likelihood is presented in the endnotes.
A.2 The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.
Some people say that recent changes to the climate are nothing new. The earth is always heating up and cooling down. To a certain extent, they are correct. The IPCC scientists are saying that the changes we are seeing today are unprecedented. Nothing like this has happened to the climate in over hundreds, even thousands of years.
A.3 Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the [IPCC’s] Fifth Assessment Report (AR5) [published in 2014].
Generally, climate is measured in decades, centuries, and millennia. Climate looks at long-term trends, not particular weather events. The weather on a given day, hot-cold-rainy-dry, is not climate. Ordinarily, climate scientists would never-ever say that a particular weather event is climate. Here they are saying, human-induced climate change in fact is affecting our weather. This indicates the enormity of the problem.
Tropical cyclones is fancy meteorology-speak for hurricanes (tropical storms that form over the North Atlantic Ocean), cyclones (formed over the South Pacific and Indian Oceans) and typhoons (formed over the northwest Pacific Ocean).
A.4 Improved knowledge of climate processes, paleoclimate evidence and the response of the climate system to increasing radiative forcing gives a best estimate of equilibrium climate sensitivity of 3°C, with a narrower range compared to AR5.
If you are wondering why the IPCC scientists are taking the positions they are taking today, and why that is different from five or ten years ago, it’s because more science is being accumulated, the mathematical models today are better than they were years ago, and science is marching on. In fact, in 1990, the IPCC said “to improve our predictive capability” it would need to better understand climate-related processes, improve observations on a global basis, develop better models to understand and predict the climate system, and obtain better international cooperation to share climate-related data. In the thirty years since the first IPCC report, there is a greater understanding of the processes, observations have vastly improved, models are infinitely better and nations readily share climate data. Keep in mind, the world’s first weather satellite, TIROS-1, was launched by NASA in 1960. The first Cray supercomputers came to market in 1964. While that was sixty years ago, in many respects, it was just a blink of the eye.
B. Possible Climate Futures
B.1. Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.
Hidden in this “headline” is bad news. Global warming of 1.5°C to 2°C is considered extremely dangerous for all of us. This will occur under the best-case scenario and it is not likely we will see the best case scenario. Governments will not have the political courage to do what is necessary to achieve that.
Scientists prefer using the metric system. The conversion to Fahrenheit is X0C times 9/5= oF. So, 1.5°C equals 2.7oF and 2°C equals 3.6oF. This is the last time I plan to do this conversion.
B.2 Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.
Changes to our climate will get worse as global warming increases. That drought/forest fire in the western US and Canada? Those floods in Europe and Greece? Those hurricanes in Puerto Rico, Texas, and Florida? Those are the G-rated previews. What will occur in the coming few years will be worse as the earth continues to warm.
B.3 Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.
The water cycle is a way of thinking about the continuous movement of water within the earth and atmosphere. It is a complex system that includes many different factors. Liquid water evaporates into water vapor, condenses to form clouds, and precipitates back to earth in the form of rain and snow. Water in different phases moves through the atmosphere (transportation). Liquid water flows across land (runoff), into the ground (infiltration and percolation), and through the ground (groundwater). The IPCC means that both the wet and dry parts of the cycle will be worse. Weather events are going to be more extreme.
B.4 Under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere.
The oceans and land act as natural sinks that hold carbon and keeps it or delays it from entering the atmosphere. Think of those sinks as nearly full, yet carbon continues to pour in. It’s just like your kitchen sink. Your sink can only hold so much water. If water is pouring into it, eventually the water will overflow and make a mess on your floor. In the carbon case, that means as the sinks fill up, the carbon will overflow and enter the atmosphere more rapidly than it does now.
B.5 Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.
The key word here is “irreversible.” This part means our kids and their kids are screwed no matter what anyone does. We did that to them. Too much has changed and some of it is irreversible. Too much ice has melted and it’s not coming back until the next ice age. The oceans are too hot and it will take generations for them to cool off. Sea levels are rising and will continue to do so. Among other things, more water in the ocean means your beachfront property was not a great long-term investment. This, in part, is why Greta Thunberg, the young Swedish climate change activist, is so pissed off. She has a right to be.
- Climate Information for Risk Assessment and Regional Adaptation
C.2 With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers. Changes in several climatic impact-drivers would be more widespread at 2° C compared to 1.5° C global warming and even more widespread and/or pronounced for higher warming levels.
Every region on earth will be affected by climate change. It is not just going to affect one area. The more warming, the worse the impact.
C.3 Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and warming substantially larger than the assessed very likely range of future warming cannot be ruled out and are part of risk assessment.
The scientists acknowledge that some events are not likely to occur. These include ice sheet collapse, abrupt ocean circulation changes, and others. Although these are low-probability outcomes, if they were to occur, the results could be dire. At one time they said they were so unlikely they ruled them out even as remote possibilities. Not anymore. While still unlikely, now they are including them in the risk assessment.
D. Limiting Future Climate Change
D.1 From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in CH4 emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.
If, somehow, the nations of the earth achieved net zero CO2 and methane (CH4, how long has it been since you took chemistry?) emissions, this would slow the warming effect, not eliminate it. Reductions in methane would also reduce warming and would improve air quality.
D.2 Scenarios with low or very low greenhouse gas (GHG) emissions lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios. Under these contrasting scenarios, discernible differences in trends of global surface temperature would begin to emerge from natural variability within around 20 years, and over longer time periods for many other climatic impact-drivers (high confidence).
If greenhouse gas emissions are lowered immediately then increasing warming and worsening air quality will improve “within years.” Note that the IPCC says they have a high confidence in this statement. This means the scientists are quite confident about this statement.
Summary for Policymakers
The headlines are dire. They are, however, the summary of the summary. The IPCC boiled down their full multi-thousand page report into a 41-page summary for policymakers. The summary is fairly technical and gets into the weeds a bit (not as much as the full report, but enough to gain an understanding of the concerns of the scientists).
The focus of the remainder of this Explainer is on the Summary for Policymakers. Let’s look at the first and key finding, of fact, in the report:
- It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.
I talked about this before, since it was also a headline (A.1). Let me repeat, “It is unequivocal that human influence has warmed the atmosphere, ocean and land.”
A.1.1 Observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 are unequivocally caused by human activities. Since 2011 (measurements reported in AR5), concentrations have continued to increase in the atmosphere, reaching annual averages of 410 ppm for carbon dioxide (CO2), 1866 ppb for methane (CH4), and 332 ppb for nitrous oxide (N2O) in 2019. Land and ocean have taken up a near-constant proportion (globally about 56% per year) of CO2 emissions from human activities over the past six decades, with regional differences (high confidence).
Pretty simple, no? Since 1750, increases in greenhouse gas are unequivocally caused by human activities. That is a strong statement. (See the endnote for how the IPCC uses terms like unequivocal, very likely, confidence levels, etc.).Greenhouse gas concentrations continue to rise. Land and oceans continue to act as sinks for carbon.
The scientific measurement of ppm stands for parts per million and ppb is parts per billion. Fun fact: one part per million is a thousand times larger than one part per billion.
A.1.2 Each of the last four decades has been successively warmer than the previous decade. Human influence has warmed the climate at a rate that is unprecedented in at least the last 2000 years. Observed warming is driven by emissions from human activities, with greenhouse gas warming partly masked by aerosol cooling.
I’m not sure this needs an explanation. The 2010s were warmer than the 2000s, which were warmer than the 1990s. Get it? Yes, your backyard was not all that warm. The IPCC’s scientists were looking at global trends. The rate of warming is unprecedented.
I’m skipping the next few sections, not because they aren’t important, they are, but just to keep this Explainer moving along. I’ve taken editorial liberties like this throughout the Summary report.
A.2 The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.
Self-explanatory. The size of climate change is unprecedented. The number of changes observed have not occurred in centuries or millennia.
A.2.1 In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years (high confidence), and concentrations of CH4 and N2O were higher than at any time in at least 800,000 years (very high confidence). Since 1750, increases in CO2 (47%) and CH4 (156%) concentrations far exceed, and increases in N2O (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years (very high confidence).
Again, mostly self-explanatory. Carbon dioxide levels are higher now than at any time in the last two million years. Methane and nitrous oxide (N2O) are at their highest levels in 800,000 years. (Yes, N2O is laughing gas, which comes not from your friendly dentist, but from agricultural and industrial sources. It is the third most significant greenhouse gas and depletes ozone in the atmosphere, which contributes to global warming.)
A.2.2 Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years (high confidence). Temperatures during the most recent decade (2011–2020) exceed those of the most recent multi-century warm period, around 6500 years ago [0.2°C to 1°C relative to 1850–1900] (medium confidence). Prior to that, the next most recent warm period was about 125,000 years ago when the multi-century temperature [0.5°C to 1.5°C relative to 1850–1900] overlaps the observations of the most recent decade (medium confidence).
Self-explanatory. The IPCC scientists are highly confident that global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years. The period 2011 to 2020, was the warmest decade since around 6500 years ago. The next most recent warm period was about 125,000 years ago.
A.2.3 In 2011–2020, annual average Arctic sea ice area reached its lowest level since at least 1850 (high confidence). Late summer Arctic sea ice area was smaller than at any time in at least the past 1000 years (medium confidence). The global nature of glacier retreat, with almost all of the world’s glaciers retreating synchronously, since the 1950s is unprecedented in at least the last 2000 years (medium confidence).
This is self-explanatory. Annual average arctic sea ice is at its lowest level since 1850. Late summer arctic sea ice area is smaller than at any time in at least the past 1000 years. Almost all of the world’s glaciers have been retreating since the 1950s. This means more, however, than giving tourists less to look at on their Alaskan cruises. The melting of these glaciers and thinning of sea ice increases the volume of water in the oceans, raises sea levels along shore, releases entrapped carbon found in the ice, reduces habitat for exiting species, and more.
A.2.4 Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3000 years (high confidence). The global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago) (medium confidence). A long-term increase in surface open ocean pH occurred over the past 50 million years (high confidence), and surface open ocean pH as low as recent decades is unusual in the last 2 million years (medium confidence).
All of this is fairly self-explanatory. The pH thing relates to the level of acid/base of the ocean. According to IPCC, ocean water pH has increased (i.e. become more alkaline or basic) over the past 50 million years. Now, scientists are observing low pH readings (i.e. more acidic). All plants and animals survive at certain pH levels. An increase in acidity could have a huge impact on plants, fish and other sea creatures. This is only a big deal if you are a fisherman, dependent or the fishing industry, or eat fish, as most of the earth’s population does at one time or another.
A.3 Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since AR5.
Self-explanatory. Climate change—caused by human activity—is already affecting weather and climate extremes throughout the world. Since 2014 (the date of the last IPCC assessment), the evidence of changes in extremes has become stronger. Here is a table I found on the internet of acres burned in California since 2014. While 2019 was an aberration as “only” 260,000 acres burned, you get the picture. In 2021, in the midst of an awful forest fire year, fire has already consumed one million acres:
A.3.1 It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe, with high confidence that human-induced climate change is the main driver of these changes. Some recent hot extremes observed over the past decade would have been extremely unlikely to occur without human influence on the climate system. Marine heatwaves have approximately doubled in frequency since the 1980s (high confidence), and human influence has very likely contributed to most of them since at least 2006.
Again, this is self-explanatory. Since the 1950s, heat waves have become more frequent and severe due to human-caused climate change. I find it interesting that the IPCC mixes weather with climate. I’m sure this is intentional and illustrates both the severity of the climate change problem and the interrelationship between weather and climate.
A.3.2 The frequency and intensity of heavy precipitation events have increased since the 1950s over most land area for which observational data are sufficient for trend analysis (high confidence), and human-induced climate change is likely the main driver. Human-induced climate change has contributed to increases in agricultural and ecological droughts in some regions due to increased land evapotranspiration (medium confidence).
The scientists have high confidence that human-caused climate change has resulted in more frequent and intense precipitation events. Likewise, climate change has contributed to increases in droughts in some regions.
A.3.5 Human influence has likely increased the chance of compound extreme events since the 1950s. This includes increases in the frequency of concurrent heatwaves and droughts on the global scale (high confidence); fire weather in some regions of all inhabited continents (medium confidence); and compound flooding in some locations (medium confidence).
Human influence has likely increased the chance of compound extreme events since the 1950s. Compound extreme events are the combination of multiple drivers and/or hazards that contribute to environmental risk. Examples are concurrent heatwaves and droughts, a storm surge in combination with extreme rainfall and/or river flow), and compound fire weather conditions (i.e., a combination of hot, dry, and windy conditions). The IPCC says it has high confidence that increases in the frequency of concurrent heatwaves and droughts on the global scale are caused by climate change; fire weather in some regions of all inhabited continents (medium confidence); and compound flooding in some locations (medium confidence).
A.4 Improved knowledge of climate processes, paleoclimate evidence and the response of the climate system to increasing radiative forcing gives a best estimate of equilibrium climate sensitivity of 3°C with a narrower range compared to AR5.
A.4.1 Human-caused radiative forcing of 2.72 [1.96 to 3.48] W m–2 in 2019 relative to 1750 has warmed the climate system. This warming is mainly due to increased GHG concentrations, partly reduced by cooling due to increased aerosol concentrations. The radiative forcing has increased by 0.43 W m–2 (19%) relative to AR5, of which 0.34 W m–2 is due to the increase in GHG concentrations since 2011. The remainder is due to improved scientific understanding and changes in the assessment of aerosol forcing, which include decreases in concentration and improvement in its calculation (high confidence).
Some people (non-scientists. politicians, talk-show hosts) complain that scientists say one thing one year and another the next (e.g. don’t wear a mask, then wear a mask). They view this as a failure of the scientists, politics, or outright lying. What they missed in high school chemistry and biology is that scientific knowledge expands and grows every day. New experiments are run, new scientific equipment becomes available, new mathematical models are developed. Here’s an example. Remember that nifty Commodore SX-64 computer you had as a kid? The computer geeks figured out how to make it better and today it is a relic for the Smithsonian. That doesn’t mean that your dad lied to you when he said it was the best machine available. It may have been in 1984. Computer science moved on. The same with climate science. What climate scientists understand today is light years ahead of what they understood in 1990. I shouldn’t have to explain this, but I just did. Sorry.
A.4.3 Heating of the climate system has caused global mean sea level rise through ice loss on land and thermal expansion from ocean warming. Thermal expansion explained 50% of sea level rise during 1971–2018, while ice loss from glaciers contributed 22%, ice sheets 20% and changes in land water storage 8%. The rate of ice sheet loss increased by a factor of four between 1992–1999 and 2010–2019. Together, ice sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006-2018. (high confidence.)
This is easy. Climate change has hearted the air. The warm air has melted glaciers and polar ice sheets. When that water melted it ran into the ocean. This has caused sea levels to rise around the world. The IPCC says it has high confidence that ice sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006-2018.
B. Possible Climate Futures
B.1 Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered (i.e. including immediate very low and low GHG emissions and CO2 emissions declining to net zero around or after 2050). Global warming of 1.5° C and 2° C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.
No matter what is done at this point, global temperatures will continue to rise until about 2050. This means, it is too late to stop some of the most immediate effects of climate change.
Stop and think about that.
If measures are taken to reduce greenhouse gases, then temperature changes may be stopped or reduced. The less that is done, the more severe the rise in temperature.
Ultimately, this reduction would have a profound effect on ice melt, sea levels, rain events, storms and droughts. The degree of that effect will depend upon the amount of reduction of greenhouse gases.
B.1.1 Compared to 1850–1900, global surface temperature averaged over 2081–2100 is very likely to be higher by 1.0°C to 1.8°C under the very low GHG emissions scenario considered by 2.1°C to 3.5°C in the intermediate scenario and by 3.3°C to 5.7°C under the very high GHG emissions scenario. The last time global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago (medium confidence).
This is self-explanatory.
B.1.2 Based on the assessment of multiple lines of evidence, global warming of 2°C, relative to 1850– 1900, would be exceeded during the 21st century under the high and very high GHG emissions scenarios considered in this report. Global warming of 2°C would extremely likely be exceeded in the intermediate scenario. Under the very low and low GHG emissions scenarios, global warming of 2°C is extremely unlikely to be exceeded, or unlikely to be exceeded. Crossing the 2°C global warming level in the mid-term period (2041–2060) is very likely to occur under the very high GHG emissions scenario, likely to occur under the high GHG emissions scenario , and more likely than not to occur in the intermediate GHG emissions scenario.
This is self-explanatory.
B.1.3 Global warming of 1.5°C relative to 1850-1900 would be exceeded during the 21st century under the intermediate, high and very high scenarios considered in this report. Under the five illustrative scenarios, in the near term (2021-2040), the 1.5°C global warming level is very likely to be exceeded under the very high GHG emissions scenario, likely to be exceeded under the intermediate and high GHG emissions scenarios, more likely than not to be exceeded under the low GHG emissions scenario and more likely than not to be reached under the very low GHG emissions scenario. Furthermore, for the very low GHG emissions scenario, it is more likely than not that global surface temperature would decline back to below 1.5°C toward the end of the 21st century, with a temporary overshoot of no more than 0.1°C above 1.5°C global warming.
This is self-explanatory. The important message here is if greenhouse gases are reduced to the low emissions scenario, global temperature will begin to decline “toward the end of the 21st century.”
B.1.4 Global surface temperature in any single year can vary above or below the long-term human-induced trend, due to substantial natural variability. The occurrence of individual years with global surface temperature change above a certain level, for example 1.5°C or 2ºC, relative to 1850–1900 does not imply that this global warming level has been reached.
The IPCC expects temperatures to vary from the curve in the model. It may be higher—or lower—than expected in any given year. The overall trend will be higher as greenhouse gas emissions continue unabated.
B.2 Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.
What does an increase in temperature mean? The hotter the average temperature becomes, the greater the likelihood of extreme heat, heavy precipitation, droughts and hurricanes. Also, the earth will experience reductions in Arctic sea ice, snow cover and permafrost.
B.2.1 It is virtually certain that the land surface will continue to warm more than the ocean surface (likely 1.4 to 1.7 times more). It is virtually certain that the Arctic will continue to warm more than global surface temperature, with highconfidence above two times the rate of global warming.
This is self-explanatory.
B.2.2 With every additional increment of global warming, changes in extremes continue to become larger. For example, every additional 0.5°C of global warming causes clearly discernible increases in the intensity and frequency of hot extremes, including heatwaves (very likely), and heavy precipitation (high confidence), as well as agricultural and ecological droughts in some regions (high confidence). Discernible changes in intensity and frequency of meteorological droughts, with more regions showing increases than decreases, are seen in some regions for every additional 0.5°C of global warming (medium confidence). Increases in frequency and intensity of hydrological droughts become larger with increasing global warming in some regions (medium confidence). There will be an increasing occurrence of some extreme events unprecedented in the observational record with additional global warming, even at 1.5°C of global warming. Projected percentage changes in frequency are higher for rarer events (high confidence).
B.2.4 It is very likely that heavy precipitation events will intensify and become more frequent in most regions with additional global warming. At the global scale, extreme daily precipitation events are projected to intensify by about 7% for each 1°C of global warming (high confidence). The proportion of intense tropical cyclones (categories 4-5) and peak wind speeds of the most intense tropical cyclones are projected to increase at the global scale with increasing global warming (high confidence).
This is self-explanatory. When the IPCC talks about “tropical cyclones” they are referring to hurricanes and typhoons. As temperatures rise, there will be more intense hurricanes and typhoons. The IPCC has a high confidence in this finding.
B.3 Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.
This is self-explanatory.
B.3.2 A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding or drought (high confidence), but the location and frequency of these events depend on projected changes in regional atmospheric circulation, including monsoons and mid-latitude storm tracks. It is very likely that rainfall variability related to the El Niño–Southern Oscillation is projected to be amplified by the second half of the 21st century.
With high confidence, IPCC projects that as the climate warms, very wet and very dry events will intensify and floods and droughts will worsen. They cannot predict the exact location where these everts will occur. The El Niño effect is a climate pattern of unusual warming of surface waters in the eastern Pacific Ocean. This results in severe drought and associated food insecurity, flooding, rains, and temperature rise. Southern Oscillation is the related air pressure of the overlying atmosphere across the equatorial Pacific Ocean. IPCC projects (very likely) that this will worsen over the rest of the century.
B.4 Under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere.
In other words, the ability of the planet to absorb and hold CO2 will diminish as CO2 in the atmosphere increases. This will result in a speeding up of accumulation of CO2 in the atmosphere.
B.5 Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.
This section, B.5, heals with changes that are irreversible “for centuries or millennia.
B.5.1 Past GHG emissions since 1750 have committed the global ocean to future warming (high confidence). Over the rest of the 21st century, likely ocean warming ranges from 2–4 to 4–8 times the 1971–2018 change. Based on multiple lines of evidence, upper ocean stratification (virtually certain),ocean acidification (virtually certain) and ocean deoxygenation (high confidence) will continue to increase in the 21st century, at rates dependent on future emissions. Changes are irreversible on centennial to millennial time scales in global ocean temperature (very high confidence), deep ocean acidification (very high confidence) and deoxygenation (medium confidence).
Because so much carbon has already entered the atmosphere and the earth has already warmed to excessive levels, certain changes cannot be stopped (measured in hundreds or thousands of years) regardless of what we do now. These changes include global ocean temperature (very high confidence), deep ocean acidification (very high confidence) and deoxygenation (medium confidence). These changes will have a profound effect on sea life, fisheries, and the ability of oceans to absorb CO2.
B.5.2 Mountain and polar glaciers are committed to continue melting for decades or centuries (very high confidence).Loss of permafrost carbon following permafrost thaw is irreversible at centennial time scales(high confidence). Continued ice loss over the 21st century is virtually certain for the Greenland Ice Sheet and likely for the Antarctic Ice Sheet. There is high confidence that total ice loss from the Greenland Ice Sheet will increase with cumulative emissions. There is limited evidence for low-likelihood, high-impact outcomes (resulting from ice sheet instability processes characterized by deep uncertainty and in some cases involving tipping points) that would strongly increase ice loss from the Antarctic Ice Sheet for centuries under high GHG emissions scenarios.
Mountain and polar (arctic) glaciers are toast. They will continue melting for decades or centuries. Likewise polar and sub-polar regions will continue to lose permafrost carbon following permafrost thaw. That is irreversible for hundreds of years. The Greenland Ice Sheet will continue to lose ice over the 21st century (virtually certain) and it is likely, the Antarctic Ice Sheet will lose ice. The IPCC has high confidence that with an increase in emissions, the Greenland Ice Sheet will experience a total loss of ice. So far as the Antarctic ice sheet is concerned, the IPCC says there is a limited chance of catastrophic loss of ice.
B.5.3 It is virtually certain that global mean sea level will continue to rise over the 21st century. Relative to 1995-2014, the likely global mean sea level rise by 2100 is 0.28-0.55 m under the very low GHG emissions scenario, 0.32-0.62 m under the low GHG emissions scenario, 0.44-0.76 m under the intermediate GHG emissions scenario, and 0.63-1.01 m under the very high GHG emissions scenario, and by 2150 is 0.37-0.86 m under the very low scenario, 0.46-0.99 m under the low scenario, 0.66-1.33 m under the intermediate scenario, and 0.98-1.88 m under the very high scenario (medium confidence). Global mean sea level rise above the likely range –approaching 2 m by 2100 and 5 m by 2150 under a very high GHG emissions scenario (low confidence) –cannot be ruled out due to deep uncertainty in ice sheet processes.
The IPCC says it is virtually certain that mean sea levels will rise around the globe. This rise will be continuous. By 2050, the range of mean sea level rise will range—with the very low greenhouse gas emissions scenario—from 1.21 feet to 2.82 feet and — under the very high scenario—from 3.22 feet to 6.16 feet. This difference can only be controlled by a concerted international effort to reduce greenhouse gases. Currently: Miami is listed as 6.562 feet above mean sea level; New Orleans is minus 6.5 to 20 feet above mean sea level. Venice, Italy is listed at 3.281 feet above sea level, however 70% of that city is below sea level. A number of Pacific Island nations are just a couple of feet above mean sea level. All coastal cities are vulnerable to inundation (in whole or in part) by rising sea levels.
B.5.4 In the longer term, sea level is committed to rise for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and will remain elevated for thousands of years (high confidence). Over the next 2000 years, global mean sea level will rise by about 2 to 3 m if warming is limited to 1.5°C, 2 to 6m if limited to 2°C and 19 to 22 m with 5°C of warming, and it will continue to rise over subsequent millennia (low confidence).
Unless dramatic action is taken, sea levels will continue to rise and will inundate areas that currently are considered inland areas.
- Climate Information for Risk Assessment and Regional Adaptation
Sorry. I skipped this section, not because it isn’t important, it is, but because I had to pare down somewhere and this seemed like the best place to cut. The IPCC describes this section as follows. I suggest you review the summary to better understand it:
Physical climate information addresses how the climate system responds to the interplay between human influence, natural drivers and internal variability. Knowledge of the climate response and the range of possible outcomes, including low-likelihood, high impact outcomes, informs climate services – the assessment of climate-related risks and adaptation planning. Physical climate information at global, regional and local scales is developed from multiple lines of evidence, including observational products, climate model outputs and tailored diagnostics.
D. Limiting Future Climate Change
D.1 From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in CH4 emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.
D.1.1 This Report reaffirms with high confidence the AR5 finding that there is a near-linear relationship between cumulative anthropogenic CO2 emissions and the global warming they cause.
The good news is (yes there is good news) if greenhouse gas emissions are quickly and sufficiently reduced, the effect of climate change will be reduced.
Carbon Capture and Sequestration
D.1.4 Anthropogenic CO2 removal (CDR) has the potential to remove CO2 from the atmosphere and durably store it in reservoirs (high confidence). CDR aims to compensate for residual emissions to reach net zero CO2 or net zero GHG emissions or, if implemented at a scale where anthropogenic removals exceed anthropogenic emissions, to lower surface temperature. CDR methods can have potentially wide-ranging effects on biogeochemical cycles and climate, which can either weaken or strengthen the potential of these methods to remove CO2 and reduce warming, and can also influence water availability and quality, food production and biodiversity (high confidence).
Carbon dioxide removal (CDR) has the potential to remove CO2 from the atmosphere and durably store it in reservoirs. A variety of techniques either exist or are the subject of experiments to achieve CDR (also known as carbon capture and sequestration).
There are several problems with this solution. IPCC says removals must exceed anthropogenic emissions. This is not yet remotely feasible. The cost of removal is still quite high. While it may be implemented on a case-by-case basis, it is not likely the CDR techniques will be widely available for many years to come. Also, some techniques involve controversial processes, like deep underground injection of carbon dioxide. The effectiveness of this has not been fully studied.
Keep in mind the IPCC report is the physical science report, not the economic/costs report. So the physical science questions are being answered, not the economic ones.
D.1.5 Anthropogenic CO2 removal (CDR) leading to global net negative emissions would lower the atmospheric CO2 concentration and reverse surface ocean acidification (high confidence). Anthropogenic CO2 removals and emissions are partially compensated by CO2 release and uptake respectively, from or to land and ocean carbon pools (very high confidence). CDR would lower atmospheric CO2 by an amount approximately equal to the increase from an anthropogenic emission of the same magnitude (high confidence). The atmospheric CO2 decrease from anthropogenic CO2 removals could be up to 10% less than the atmospheric CO2 increase from an equal amount of CO2 emissions, depending on the total amount of CDR (medium confidence).
CDR could be effective at removing CO2 from the atmosphere and restoring some of the impact caused by climate change. It is possible, however, thatCO2 removals would be offset by an increase of up to 10% as sinks release CO2 back into the atmosphere.
D.1.6 If global net negative CO2 emissions were to be achieved and be sustained, the global CO2-induced surface temperature increase would be gradually reversed but other climate changes would continue in their current direction for decades to millennia (high confidence). For instance, it would take several centuries to millennia for global mean sea level to reverse course even under large net negative CO2 emissions (high confidence).
If CO2 emissions could be reduced to zero, temperature increases would gradually be reversed. Other changes to climate, however, would continue “for decades or millennia.” This would include global mean sea level increases, which will take hundreds or thousands of years to “reverse course.”
D.2 Scenarios with very low or low GHG emissions lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios. Under these contrasting scenarios, discernible differences in trends of global surface temperature would begin to emerge from natural variability within around 20 years, and over longer time periods for many other climatic impact-drivers (high confidence).
If greenhouse gases are reduced to low or very low levels, there will be discernable reductions of the effects on greenhouse gas concentrations. With a high confidence level, IPCC says over a period of around 20 years, “discernable differences” in trends of global surface temperatures would begin to emerge.
D.2.1 Emissions reductions in 2020 associated with measures to reduce the spread of COVID-19 led to temporary but detectible effects on air pollution (high confidence), and an associated small, temporary increase in total radiative forcing, primarily due to reductions in cooling caused by aerosols arising from human activities (medium confidence). Global and regional climate responses to this temporary forcing are, however, undetectable above natural variability (high confidence). Atmospheric CO2 concentrations continued to rise in 2020, with no detectable decrease in the observed CO2 growth rate (medium confidence).
COVID-19 provided an unexpected laboratory to see what impacts would emerge from significant short-term reductions of greenhouse gases. Measures taken to reduce the spread of COVID-19 (lock-downs) resulted in detectible, albeit temporary, effects on air pollution. According to IPCC, during the lock-down phase of COVID-19, global and regional differences in climate change were undetectable above natural variability. Furthermore, atmospheric CO2 concentrations continued to rise in 2020.
D.2.2 Reductions in GHG emissions also lead to air quality improvements. However, in the near term, even in scenarios with strong reduction of GHGs, as in the low and very low GHG emission scenarios, these improvements are not sufficient in many polluted regions to achieve air quality guidelines specified by the World Health Organization (high confidence). Scenarios with targeted reductions of air pollutant emissions lead to more rapid improvements in air quality within years compared to reductions in GHG emissions only, but from 2040, further improvements are projected in scenarios that combine efforts to reduce air pollutants as well as GHG emissions with the magnitude of the benefit varying between regions (high confidence).
IPCC notes that as greenhouse gases are reduced, that should result in improvements to air quality. Unfortunately, even with low to very low greenhouse gas emissions, the improvements will not meet World Health Organization guidelines for air quality in many polluted regions.
Conclusion
Call the IPCC report a “wake-up call” or a blaring Klaxon warning residents of Planet Earth to take action. It’s not “fake news.” This is science. IPCC’s Physical Science Report of the Sixth Assessment Report states unequivocally, the nations of the earth must take action to reduce and eliminate greenhouse gases from the atmosphere. This time for debate is over. We may be too late.
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If you want to take a deep dive into climate change as discussed by genuine climate scientists, have a look at the website RealClimate: Climate Science from Climate Scientists. https://www.realclimate.org/
ENDNOTE
Confidence and Certainty
The IPCC developed “guidance notes” to assist the various teams that worked on the IPCC reports. This were intended to assist Lead Authors of the Fifth Assessment Report (AR5) in the consistent treatment of uncertainties (July 6, 2010). These notes define a common approach and calibrated language that can be used broadly for developing expert judgments and for evaluating and communicating the degree of certainty in findings of the assessment process. The guidance utilized similar guidance documents developed for earlier IPCC reports.
Two different terms are used: “confidence” and “certainty.”
A level of confidence is expressed using five qualifiers: “very low,” “low,” “medium,” “high,” and “very high.” It synthesizes the author teams’ judgments about the validity of findings as determined through evaluation of evidence and agreement…Increasing levels of evidence and degrees of agreement are correlated with increasing confidence. Confidence cannot necessarily be assigned for all combinations of evidence and agreement… Confidence should not be interpreted probabilistically, and it is distinct from “statistical confidence.” Additionally, a finding that includes a probabilistic measure of uncertainty does not require explicit mention of the level of confidence associated with that finding if the level of confidence is “high” or “very high.”
Likelihood is different than confidence. It relates to the likelihood of a particular outcome. The table below illustrates what the IPCC means by different levels of likelihood:
