The Changing Climate: Part 3 (2021 IPCC Report)

by Rick O'Connor | Sep 23, 2021

In Part 3 we are going to look at the most recent Assessment Report No.6 (AR6) published by the Intergovernmental Panel on Climate Change.  This document is 3,946 pages – so, we will focus only on the executive summary for policy makers.  This summary circles on the key points of the report.  It was published August 7, 2021.

Sunrise over Apalachicola Bay in Northwest Florida

The Intergovernmental Panel on Climate Change

Who is the IPCC?

It is a panel developed by the United Nations to address the topic of global climate change.  It was created in 1988 by the World Meteorological Organization and the United Nations Environmental Programme.  It currently has 195 members and contributions from thousands of scientists.  The panel scientists volunteer their time to review all of the scientific papers that are used in the assessment reports.  The panel meets one or more times a year¹.

IPCC Assessment Report Six (AR6) – August 7, 2021

All of the assessment reports are based on scientific information and presented as statements of fact, or statements at a level of confidence using an IPCC calibrated language (such as likely, medium confidence, high confidence, etc.).  The summary for policy makers is divided into four sections.  We will summarize each one.

1. Current State of the Climate
2. Possible Climate Futures
3. Climate Information for Risk Assessment and Regional Adaptation
4. Limiting Future Climate Change

1. 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. 

The definition of unequivocal is “leaving no doubt, unquestionable, clear”.  Using that term here indicates the panel is convinced that the current warming of our planet is caused by human activity.  Thus, there is something we can do to turn it around.

Other statements in this section include:

• Each of the last four decades has been successively warmer than any decade preceded it since 1850.
• Globally averaged precipitation over land has likely increased since 1950, with a faster rate of increase since the 1980s.

This term likely is one of the terms used by their calibrated language model.  Suggesting the confidence level is not as high – but likely.

• It is likely that human influence contributed to the pattern of observed precipitation change since the mid-20^th century, and extremely likely that human influence contributed to the pattern of observed changes in near-surface ocean salinity.
• Mid-latitude storm tracks have likely shifted poleward in both hemispheres since the 1980s.
• Human influence is very likely the main driver of the global retreat of glaciers since the 1990s and the decrease in the Arctic Sea ice area between 1979-1988 and 2010-2019 is about 40% in September and 10% in March.
• It is virtually certain that the global upper ocean (0-2400 feet) has warmed since the 1970s and extremely likely that human influence is the main driver.
• Global mean sea level increased by 0.7 feet between 1901 and 2018.
• Changes in land ecosystems since 1970 are consistent with global warming. Climate zones have shifted poleward in both hemispheres and growing seasons have, on average, lengthened by up to two days per decade since the 1950s.  This is stated with high confidence.

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 thousand years. 

• In 2019, atmospheric CO₂ concentrations were higher than at any time in at least 2 million years (high confidence), and concentrations of CH₄ (methane) and N₂O (nitrous oxide) were higher than at any time in at least 800,000 years (very high confidence).
• Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years (high confidence).
• In 2011-2020, annual average Arctic Sea ice area reached its lowest level since at least 1850 (high confidence).
• Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3000 years (high confidence).

A.3) Human-Induced climate change is already affecting many weather and climate extremes in every region across the globe.  Evidence in observed changes in extremes such as heatwaves, heavy precipitation, droughts, tropical cyclone, and (in particular) their attribution to human influence, has strengthen since AR5.

• It is virtually certain that hot extremes have become more frequent and more intense across most land regions since the 1950s, while cold extremes have become less frequent and less severe, and that human-induced climate change is the main driver (high confidence).
• 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 the main driver (likely).
• It is likely that the global proportion of major (Category 3-5) tropical cyclone occurrence has increased over the last four decades, and the latitude where the cyclones reach their peak intensity has shifted northward. These changes cannot be explained by internal variability alone (medium confidence).  There is low confidence in long-term (multi-decade to centennial) trends in the frequency of all-category tropical cyclones.  Event attribution studies and physical understanding indicate that human-induced climate change increases heavy precipitation associated with tropical cyclones (high confidence), but data limitations inhibit clear detection of past trends on the global scale.
• Human influence has likely increased the chance of compound extreme events since the 1950s.

1. Possible Climate Futures

B1. 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 21^st century unless deep reduction in CO₂ and other greenhouse gas emissions occur in the coming decades.

• Compared to 1850-1900, global surface temperature averaged over 2081-2100 is very likely to be higher than 1.0°C to 1.8°C under the VERY LOW greenhouse gas emissions scenario. 1°C – 3.5°C in the INTERMEDIATE scenario.  And 3.3°C to 5.7°C under the VERY HIGH scenario.
• Global surface temperature in any single year can vary above or below the long-term human-induced trend, due to substantial natural variability.

B2. 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, 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.

• It is virtually certain that the land surface will continue to warm more than the ocean surface. It is virtually certain that the Arctic will continue to warm more than the global surface temperature.
• With every additional increment of global warming, changes in extremes continue to become larger.
• Some mid-latitude and semi-arid regions, and the South American Monsoon region, are projected to see the highest increase in the temperature of the hottest days, about 1.5 to 2 times the global rate of warming (high confidence).
• It is very likely that heavy precipitation events will intensify and become more frequent in most regions with additional global warming.
• Additional warming is projected to further amplify permafrost thawing, and loss of seasonal snow cover, of land ice, and of Arctic Sea ice (high confidence).

B3. Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and severity of wet and dry events.

• There is strengthened evidence since AR5 that the global water cycle will continue to intensify as global temperatures rise (high confidence), with precipitation and surface water flows projected to become more variable over most land regions within seasons (high confidence) and from year to year (medium confidence).
• A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding and droughts (high confidence), but the location and frequency will depend on projected changes in regional and atmospheric circulation, including monsoons and mid-latitude storm tracks.

B4. 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.  

• Based on model projections, under the intermediate scenario that stabilizes atmospheric CO₂ concentrations this century, the rates of CO₂ taken up by the land and oceans are projected to decrease in the second half of the 21^st century (high confidence).

B5. 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.

• Past greenhouse gas emissions since 1750 have committed the global ocean to future warming (high confidence).
• Mountain and polar glaciers are committed to continue melting for decades or centuries (very high confidence).
• It is virtually certain that global mean sea level will continue to rise over the 21^st
• In the longer term, sea level is committed to rise for centuries to millennia due to deep ocean warming and ice sheet melt and will remain elevated for thousands of years (high confidence).

1. Climate Information for Risk Assessment and Regional Adaptation

C1. Natural drivers and internal variability will modulate human-induced changes, especially at regional scales and in the near term, with little effect on centennial global warming.  The modulations are important to consider in planning for the full range of possible changes.

What this is basically stating is that the predictions made with the computer models, can be altered by natural drivers (such as nearby ocean currents, forested land, or even urban-induced weather) as well as internal variability (such as the humidity at time of cyclone formation, wind conditions during a heavy rainfall, etc.).  These are regional impacts and are not accounted for in the models.

C2. With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climate impact-drivers.  Changes in several climatic impact-drivers would be more widespread to 2°C compared to 1.5°C global warming and even more widespread and/or pronounced for higher warming levels.

Basically… as the model predictions occur, their impacts on the climate can change enough that the data inputted into the model could be warmer than anticipated and thus, increase the outcome predicted.

• It is very likely to virtually certain that regional mean relative sea level rise will continue throughout the 21st century, except in a few regions with substantial geologic land uplift rates.
• Cities intensify human-induced warming locally, and further urbanization together with more

frequent hot extremes will increase the severity of heatwaves (very high confidence).

• Many regions are projected to experience an increase in the probability of compound events with higher global warming (high confidence).

C3. Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulations changes, some compound extreme events and warming substantially larger than the assessed very likely ranges of future warming cannot be ruled out and are part of risk assessment.

Unpredictable and rare natural events not related to human influence on climate may lead to low likelihood, high impact outcomes.

1. Limiting Future Climate Change

D1. From a physical science perspective, limiting human-induced global warming to a specific level requires limiting CO₂ emissions, reaching at least net zero CO₂ emissions, along with strong reductions in other greenhouse gases.  Strong, rapid and sustained reductions in CH₄ (methane) emissions would also limit the warming effect resulting from the declining aerosol pollution and would improve air quality.

• Removing CO₂ by humans leading to net negative emissions would reverse surface ocean acidification (high confidence).
• If global net negative CO₂ emissions were to be achieved and be sustained, the global CO­₂-induced surface temperature increase would gradually reverse, but other climate change 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).

D2. Scenarios with very low or low greenhouse gas emissions lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very greenhouse gas 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 climate impact-drivers (high confidence). 

Basically… at high confidence – if we can reduce the amount of greenhouse gas emissions to match the low emission scenario used by the models, the climate outcomes would be reduced as well.

• 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).
• Scenarios with very low or low GHG emissions would have rapid and sustained effects to limit human-caused climate change, compared with scenarios with high or very high GHG emissions, but early responses of the climate system can be masked by natural variability.

SUMMARY OF THIS REPORT

1. Based on the report – there is no doubt that human-induced greenhouse gases have warmed the planet.
2. The climatic changes observed over the last century are unprecedented.
3. Weather and climate extremes are occurring.
4. No matter what we do, global surface temperatures will continue to increase until mid-century.
5. If the annual increases in greenhouse gas emissions continues, their weather/climate impacts will increase as well.
6. If emissions continue at their present rate, the carbon sinks (methods of removing carbon – both land and ocean) will become less effective.
7. With high confidence – some impacts are irreversible – oceans will continue to warm, ice sheets and glaciers will continue to melt, and sea level will continue to rise for centuries and millennia.
8. There are local and regional features (nearby ocean currents, forested – or deforested areas, nearby mountain ranges) that can alter the impacts of the computer models for better or worse, than the scenarios presented.
9. Some regional climate impacts can affect the outcomes as such as multiple events can occur.
10. By reducing greenhouse gases, we can alter some of the impacts predicted in these scenarios.

COMMENTS

Much of this sounds bad… and it is.  As we mentioned in Part 1 “everyone is talking about the climate… but no one is doing anything about it” is not 100% true… many are doing something about it.  But based on this AR6 report, not enough.  The AR6 report also mentions that many of the climate/weather scenarios can be altered if we do begin to make some behavioral changes on the amount of greenhouse gasses we emit AND look into sources of carbon sequestering.

In Part 4 of this series, we will look closer at the impacts this is having on the Florida panhandle.

The Gulf of Mexico as seen from Pensacola Beach.
Photo: Molly O’Connor

References

¹ The Intergovernmental Panel on Climate Change

https://www.ipcc.ch/

² IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis.

Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.

The Changing Climate: Part 1

by Rick O'Connor | Aug 30, 2021

Mark Twain once said – “Everyone talks about the weather, but no one does anything about it”.  I guess you could say the same for climate.

The topic has been around for a while.  As an undergrad science major in the late 1970s, we discussed what was then called “global warming”.  It was explained to us that there were gases in our atmosphere that can cause what was called “the greenhouse effect”.  Like the windows of a greenhouse, these gases allowed solar radiation to pass through to the surface of the planet but would not allow heated air to leave.  Within the greenhouse it would get warmer.

The greenhouse effect.
Image: NOAA

It was also explained to us that this was a natural part of the planet’s cycle.  That without the “greenhouse effect” life on our planet could not exist.  But it was also explained that the cycle worked like the thermostat in your home.  Conditions on the planet increased the amount of greenhouse gas, which would in turn, increase the temperature of the planet.  These warming conditions would enhance specific forms of life and their populations increased as well, land and sea.  But like a thermostat at home, when the temperature reaches a certain point, the HAVC system shuts off and a cooling period happens within the house.  The same happens on earth.  Trees, and other forms of life, would increase in number during the warming periods but consume CO₂ for photosynthesis and reduce the greenhouse effect leading to a cooling period.  Other methods of greenhouse gas sequestration would occur as well.  We know that the cooling periods could be quite significant – leading to ice ages.  The species that sequestered the greenhouse gases would decline with the cooling periods allowing for an increase in those gases, and the cycle would begin again. And so it goes.

But was there any scientific evidence that such cycles actually exist?

Yes…

It is simple to construct an experiment within a closed system in a lab where you increase selected greenhouse gases to determine whether they actually increase temperatures within the systems.  This has been numerous times by numerous scientific teams and the answer is yes… this happens.  Science has been following this since 1896¹.

Svante Arrhenius, the Swedish chemist who first proposed how the greenhouse effect works in 1896.
Image: Science History Institute.

But is there evidence this occurs in the natural world, where there are more complex factors involved?

Yes…

Probably one of the more notable ones were gases trapped in ice cores removed from Arctic and Antarctic ice.  Geology has understood for decades that material on our planet, rock and ice, are laid down over time.  You can travel anywhere out west and see these layers of different rock layered over time.  The idea is that the older material is laid down first and the newer material is near the top.  But we also have evidence that the world is not a stagnant place.  The earth’s surface shifts and changes constantly under the stresses of plate tectonics (another topic for another day).  This shifting can cause older material on the bottom to shift in an upward position, placing it at – or above – newer material.  So, geologists understand that it is not as simple as “older is on bottom” and great scrutiny and study must go into “reading” the rock layers.  But reading those rock layers correctly can tell you a lot about how the earth has changed over time.

You can see the different layers of rocks as they have laid out over the history of the earth.
Photo: Rick O’Connor

Notice the different layers within the rock face in Utah.
Photo: Rick O’Connor

This slab of rock shows the impression of a dinosaur foot. Notice how the slab has slid down the rock face into its current position.
Photo: Rick O’Connor

We know that when ice forms gas bubbles are trapped inside.  You can take any ice cube today and see this.  Using the same concept as “rock reading”, you can read layers of ice that are cored from the great ice sheets at the poles.  Analyzing these gases, you can get an idea of the concentration of the greenhouse gases present at the time the ice formed.  You can compare this to the fossilized plants and animals (even fossilized pollen) of those same periods and put together a map of the concentration of greenhouse gases, what the expected temperatures would have been based on those concentrations and compare this to the plants and animals that existed during that same time (were they warm or cold seasoned creatures).  With this you could develop a map of the changing climate over time.

An ice core is being removed by a NOAA scientist.
Photo: NOAA

There is data going back over the last 900,000 years and yes… there are cool and warm periods found.  One graph published by Miller and Spoolman (2011)¹ shows average surface temperatures ranging from 9°C to 16°C (48°F to 61°F) over the last 900,000 years.  The graph shows a basic “sine wave” of steady cooling and warming – a steady pattern – a cycle.  Miller and Spoolman referred to these cycles as glacial and interglacial periods (freezing and thawing).

So, the lab and field evidence suggest we do live on a planet with ever changing climate.  We are currently in a “thawing” period, and all is right with the world.  But the data shows something else.  Something that has climate scientists a bit concerned.  Over the last 1000 years there has been a steady increase in surface temperatures, which was expected, but over the last 100 years there has been an unusual spike in increasing temperatures, something that have not seen in all of the data studied before.  A rapid increase in surface temperature.  What could be causing this unusual steep increase, and can the natural sequestering processes mitigate this rapid change?

This graph shows the changes in mean CO2 levels over the last 800,000 years. Notice the sharp increase in recent years.
Image: NOAA

If you examine a graph of temperature change over the last 1000 years you will notice the unusual spike beginning about the year 1900, 120 years ago.  What could have happened to generate this spike?

Did the concentrations of greenhouse gases increase at the same rate during this time period?

Yes… they did.

What could have happened to cause this unusual increase in greenhouse gases and surface temperatures?  And why has the natural sequestering process to cool the planets “thermostat” not kept up?

Back to the lab and to the field.

One event stands out… the industrialization of the planet.  The industrial revolution began almost 300 years ago.  We moved from burning wood as a source of energy to coal, and eventually oil.  The burning of these fossil fuels significantly increases the same types of gases as the planet’s greenhouse gases (carbon dioxide CO₂, methane CH₄ and others).  By the turn of the century (1900) the fossil fuel boom was in full swing.  Industry and transportation were burning more and more of these fuels emitting more and more of the greenhouse gases that we know warm the planet up.

Power plant on one of the panhandle estuaries.
Photo: Flickr

But what about the sequestering processes of the forest and the oceans?

We began removing the forest.  As the human population grows there is a need for more land for agriculture and homes/cities to live in.  All across the planet deforestation was also in full swing, and agriculture/cities used fossil fuels as well.  The change was on.  Science has been able to determine that the carbon dioxide concentration has risen from 280 ppm at the beginning of the industrial revolution to 384 ppm in 2007¹.  A study conducted by Field and Marland (2007) suggested that if the rate of CO₂ increase at that time (3.3% annually) continued, it would reach 560 ppm by 2050 and 1390 ppm by 2100.  This would have a significant impact on the climate which would in turn have a significant impact on the ecology and economics of our planet.

There was deep concern over this in the scientific community.  They began developing computer models that could predict the changes in temperature with increased rates of greenhouse gases and how those could impact glacial melt, sea level rise, and atmospheric conditions that stimulate our weather.  It is understood that models are only as good as the data you provide.  We have learned this with hurricane models.  There are numerous computer models that predict the landfall of hurricanes.  The climatologist inputs what data they can get, and the model predicts where the storm will probably go – and at what intensity it will probably hit land with.  These are the classic “spaghetti” models we are all familiar with on the evening weather.  With hurricanes it is pretty easy to test your model.  You input the data – predict landfall and intensity – and see what happens.  You will get results very soon.  You will notice on the evening weather that not all models make landfall at the same location.  Some models are better than others.  For those that were wrong, you go back and determine what information was not inputted, or inputted incorrectly, and “fix the model”.  Because of this we feel very good about our hurricane models.

Hurricane forecasting has improved tremendously over the last decades.
Image: NOAA

But with climate, the results of the “landfall” will not happen in hours or days – it will be years or decades.  So, as the models were developed in the early 1980s, no one knew for certain whether they were accurate or not.

But that did not stop climate scientists from developing them.  There was much concern in what they thought might happen.  Some studies suggested that the “tipping point” (the point of no return) for CO₂ admissions was 450 ppm¹.  Their concern was CO₂ at, or above, this value could have consequences that could be irreversible for long periods of time – for some, they may never recover.  This means even if we brought CO₂ emissions down to almost zero, we would still feel the effects for years – a lag effect, and some impacts may not be corrected.  And CO₂ is only one of the greenhouse gases – there were several others that needed to be watched and analyzed as well.  This concerned many scientists as well.  Was anyone paying attention?

Enter the IPCC…

In 1988 the United Nations and the World Meteorological Organization established the International Panel on Climate Change (IPCC).  This panel consists of over 2500 climatologists from over 130 countries.  Their 2007 report was based on more than 29,000 sets of data collected over that last decade.  It was stated in this report that there was high probability (90-99%) that the lower atmosphere of the planet is warming and that human activities were responsible for most of this.  They cited multiple layers of evidence to support this statement.

This report stated that a rise of 2°C (3.6°F) over 2005 temperatures is unavoidable, and an increase of 3°C (5.4°F) is likely during the next century.  Their models suggested the possible outcomes of such climate change.

At a 2°C increase¹

• Forest fires worsen
• Prolonged droughts become more intense
• Major heat waves become more common
• Conflicts over water supplies will increase
• Modest crop production increases in temperate regions
• Crop yields fall in tropical Africa
• Coral reefs will be impacted by bleaching
• Glaciers melt faster and impact water supplies for some
• Sea levels will rise and initiate coastal flooding issues
• Malaria will increase
• Arctic species will experience an increase in extinction

At a 3°C increase¹

• Forest fires get worse
• Prolonged droughts get worse
• Deserts spread more
• Major heat waves will increase, and associated deaths with them
• Irrigation and hydroelectric power declines
• Water shortages for billions of people
• Water wars and terrorism increase
• Malaria and tropical disease will spread
• Crop pests will multiple
• Coral reefs severely threatened
• Arctic tundra will melt
• 20-30% of the species will face extinction

We discussed how many climate models need time to be tested.  It was 30 years between the time I first heard about “global warming” and the publication of the 2007 IPPC report, and another 10 years since that report came out.  Do any of the predictions in the list above look familiar?  Could these models be on the right course, as we learned with hurricane models – could these be correct?

If so, “no one is doing anything about the weather” – but are we doing anything about the climate?

In the next edition – The Changing Climate: Part 2 – we will look what has happened since 2007.  How have things changed in the last decade?  Are things getting better?

Reference

¹ Miller, G.T., S.E. Spoolman. 2011. Living in the Environment: Concepts, Connections, and Solutions.  Brooks and Cole Publishing, Belmont CA.  pp. 659.