The UN-sponsored Intergovernmental Panel on Climate Change (IPCC) recently released its latest comprehensive report on the state of the earth’s climate. The much-anticipated report dominated the headlines for a few days in early August, then quickly disappeared amidst the latest news from Afghanistan, the fourth wave of Covid-19 infections in the US, and all the latest political rumblings. The report is vast and comprehensive in its scope, and is worthy of more focused attention outside of specialist scientific circles than it has received thus far.
The report affirms much of what we already knew about the state of the global climate, but does so with considerably more clarity and precision than earlier reports. It removes several elements of uncertainty from the climate picture, including some that have wrongly served to reassure powerful interests and the wider public that things may not be as bad as we thought. The IPCC’s latest conclusions reinforce and significantly strengthen all the most urgent warnings that have emerged from the past 30 to 40 years of climate science. It deserves to be understood much more fully than most media outlets have let on, both for what it says, and also what it doesn’t say about the future of the climate and its prospects for the integrity of all life on earth.
First some background. Since 1990, the IPCC has released a series of comprehensive assessments of the state of the earth’s climate, typically every 5-6 years. The reports have hundreds of authors, run for many hundreds of pages (this one has over 3000), and represent the international scientific consensus that has emerged from the period since the prior report. Instead of releasing a comprehensive report in 2019, as originally scheduled, the IPCC followed a mandate from the UN to issue three special reports: on the implications of warming above 1.5 degrees (all temperatures here are in Celsius except where otherwise noted), and on the particular implications of climate change for the earth’s lands and oceans. Thus the sixth comprehensive Assessment Report (dubbed AR6) is being released during 2021-22 instead of two years prior. Also the report released last week only presents the work of the first IPCC working group (WGI), focused on the physical science of climate change. The other two reports, on climate impacts (including implications for health, agriculture, forests, biodiversity, etc.) and on climate mitigation—including proposed policy measures—are scheduled for release next February and March, respectively. While the basic science report typically receives far more press coverage, the second report on climate impacts and vulnerabilities is often the most revealing, describing in detail how both ecosystems and human communities will experience the impacts of climate changes.
In many respects, the new document represents a qualitative improvement over the previous Assessment Reports, both in terms of the precision and reliability of the data and also the clarity of its presentation. There are countless detailed charts and infographics, each illuminating the latest findings on a particular aspect of current climate science in impressive detail. There is also a new Interactive Atlas (freely available at interactive-atlas.ipcc.ch), which allows any viewer to produce their own maps and charts of various climate phenomena, based on a vast array of data sources and climate models.
If there is a key take-home message, it is that climate science has vastly improved over the past decade in terms of its precision and the degree of confidence in its predictions. Many uncertainties that underlay past reports appear to have been successfully addressed, for example how a once-limited understanding of the behavior and dynamics of clouds were a major source of uncertainty in global climate models. Not only have the mathematical models improved, but we now have more than thirty years of detailed measurements of every aspect of the global climate that enable scientists to test the accuracy of their models, and also to substitute direct observations for several aspects that once relied heavily upon modeling studies. So we have access to better models, and are also less fully reliant upon them.
Second, scientists’ understanding of historic and prehistoric climate trends have also vastly improved. While the IPCC’s third report in 2001 made headlines for featuring the now-famous “hockey stick” graph, showing how average temperatures had been relatively stable for a thousand years before starting to spike rapidly in the past few decades, the current report highlights the relative stability of the climate system over many thousands of years. Decades of detailed studies of the carbon contents of polar ice cores, lake and ocean sediments and other geologically stable features have raised scientists’ confidence in the stark contrast between current climate extremes and a couple of million years of relative climate stability. The long-term cycle of ice ages, for example, reflects shifts of about 50 to 100 parts per million (ppm) in atmospheric carbon dioxide concentrations, compared to a current concentration (approximately 410 ppm) that is well over 150 ppm higher than the million-year average. We need to look back to the last interglacial era (125,000 years ago) to find an extended period of high average temperatures comparable to what we are experiencing now, and current carbon dioxide concentrations in the atmosphere are believed to be higher than any time in at least two million years.
With these overarching issues in mind, it is time to summarize some of the report’s most distinctive findings and then reflect upon their implications.
First, the question of “climate sensitivity” has been one of the more contentious ones in climate science. It is a measure of how much warming would result from a doubling of atmospheric CO2 from preindustrial levels, i.e. from 280 ppm to 560 ppm. Early estimates were all over the map, giving policymakers the wiggle room to suggest it is reasonable to reduce emissions more slowly or wait for newer technologies—from better batteries to carbon capture and even nuclear fusion—to come along. This report greatly narrows the scope of that debate, with a “best estimate” that doubling CO2 will produce approximately 3 degrees of warming—far too high to avoid extremely dire consequences for all of life on earth. Climate sensitivity is very likely (more than 90% confidence) between 2—4.5 degrees and likely (2/3 confidence) between 2.5 and 4 degrees. Of the five main future scenarios explored in the report, only those where global greenhouse gas emissions reach their peak before 2050 will avoid that disastrous milestone. If emissions continue increasing at rates comparable to the past few decades, we’ll reach doubled CO2 by 2100; if emissions accelerate, it could happen in just a few decades, vastly compounding the climate disruptions the world is already experiencing.
A second key question is, how fast do temperatures rise with increasing emissions? Is it a direct, linear relationship, or might temperature rises begin to level off any time in the foreseeable future? The report demonstrates that the effect remains linear, at least up to the level of 2 degrees warming, and quantifies the effect with high confidence. Of course there are important deviations from this number (1.65 degrees per thousand gigatons of carbon): the poles heat up substantially more quickly than other regions, the air over continental land masses heats up faster than over the oceans, and temperatures are warming almost twice as fast during cold seasons than warm seasons, accelerating the loss of arctic ice and other problems. Of course more extreme events remain far less predictable, except that their frequency will continue to increase with rising temperatures. For example the triple digit (Fahrenheit) temperatures that swept the Pacific Northwest of the US and southwestern Canada this summer have been described as a once in 50,000 years event in “normal” times and no one excludes the possibility that they will happen again in the near future. So-called “compound” events, for example the combination of high temperatures and dry, windy conditions that favor the spread of wildfires, are the least predictable events of all. The central conclusion from the overall linear increase in temperatures relative to emissions is that nothing short of a complete cessation of CO2 and other greenhouse gas emissions will significantly stabilize the climate, and there is also a time delay of at least several decades after emissions cease before the climate can begin to stabilize.
Third, estimates of likely sea level rise, in both the near- and longer-terms, are far more reliable than they were a few years ago. Global sea levels rose an average of 20 centimeters during the 20th century, and will continue to rise throughout this century under all possible climate scenarios—about a foot higher than today if emissions begin to fall rapidly, nearly 2 feet if emissions continue rising at present rates, and 2.5 feet if emissions rise faster. These, of course, are the most cautious scientific estimates. By 2150 the estimated range is 2—4.5 feet, and more extreme scenarios where sea levels rise from 6 to 15 feet “cannot be ruled out due to deep uncertainty in ice sheet processes.” With glacial melting expected to continue for decades or centuries under all scenarios, sea levels will “remain elevated for thousands of years,” potentially reaching a height of between 8 and 60 feet above present levels. The last time global temperatures were comparable to today’s for several centuries (125,000 years ago), sea levels were probably 15 to 30 feet higher than they are today. When they were last 2.5 to 4 degrees higher than preindustrial temperatures—roughly 3 million years ago—sea levels may have been up to 60 feet higher than today. Again these are all cautious estimates, based on the available data and subject to stringent statistical validation. For residents of vulnerable coastal regions around the world, and especially Pacific Island dwellers who are already forced to abandon their drinking water wells due to high infiltrations of sea water, it is far from just a theoretical problem.
Also, for the first time, the new report contains detailed projections for the unfolding of various climate-related phenomena in every region of the world. There is an entire chapter devoted to regionally-specific effects, and much attention to the ways in which climate disruptions play out differently in different locations. “Current climate in all regions is already distinct from the climate of the early or mid-20th century,” the report states, and many regional differences are expected to become more pronounced over time. While every place on earth is getting hotter, there are charts showing how different regions will become consistently wetter or dryer, or various combinations of both, with many regions, including eastern North America, anticipated to experience increasingly extreme precipitation events. There are also more specific discussions of potential changes in monsoon patterns, as well as particular impacts on biodiversity hotspots, cities, deserts, tropical forests, and other places with distinctive characteristics in common. Various drought-related phenomena are addressed in more specific terms, with separate projections for meteorological drought (lack of rainfall), hydrological drought (declining water tables) and agricultural/ecological drought (loss of soil moisture). It can be expected that all these impacts will be discussed in greater detail in the upcoming report on climate impacts that is due in February.
There are numerous other important observations, many of which directly counter past attempts to minimize the consequences of future climate impacts. For those who want to see the world focus more fully on emissions unrelated to fossil fuel use, the report points out that between 64 and 86 percent of carbon emissions are directly related to fossil fuel combustion, with estimates approaching 100 percent lying well within the statistical margin of error. Thus there is no way to begin to reverse climate disruptions without an end to burning fossil fuels. There are also more detailed projections of the impacts of shorter-lived climate forcers, such as methane (highly potent, but short-lived compared to CO2), sulfur dioxide (which counteracts climate warming) and black carbon (now seen as a substantially less significant factor than before). To those who assume the vast majority of emissions will continue to be absorbed by the world’s land masses and oceans, buffering the effects on the future atmosphere, the report explains how with rising emissions, a steadily higher proportion of the CO2 remains in the atmosphere, rising from only 30 to 35 percent under low emissions scenarios, up to 56 percent with emissions continuing to increase at present rates and doubling to 62 percent if emissions begin to rise more rapidly. So we will likely see a declining capacity for the land and oceans to absorb a large share of excess carbon dioxide.
The report is also more skeptical than in the past toward geoengineering schemes based on various proposed technological interventions to absorb more solar radiation. The report anticipates a high likelihood of “substantial residual or overcompensating climate change at the regional scales and seasonal time scales” resulting from any interventions designed to shield us from climate warming without reducing emissions, as well as the certainty that ocean acidification and other non-climate consequences of excess carbon dioxide would inevitably continue. There will likely be substantially more discussion of these scenarios in the third report of this IPCC cycle, which is due in March.
In advance of the upcoming international climate conference in Glasgow, Scotland this November, several countries have pledged to increase their voluntary climate commitments under the 2015 Paris Agreement, with some countries now aiming to achieve a peak in climate-altering emissions by mid-century. However this only approaches the middle range of the IPCC’s latest projections. The scenario based on a 2050 emissions peak is right in the middle of the report’s range of predictions, and shows the world surpassing the important threshold of 1.5 degrees of average warming in the early 2030s, exceeding 2 degrees by mid-century, and reaching an average temperature increase between 2.1 and 3.5 degrees (approximately 4-6 degrees Fahrenheit) between 2080 and 2100, nearly two and a half times the current global average temperature rise of 1.1 degrees since preindustrial times.
We will learn much more about the impacts of this scenario in the upcoming February report, but the dire consequences of future warming have been described in numerous published reports in recent years, including an especially disturbing very recent paper reporting signs that the Atlantic circulation (AMOC), which is the main source of warm air for all of northern Europe, is already showing signs of collapse. If carbon emissions continue to increase at current rates, we are looking at a best estimate of a 3.6 degree rise before the end of this century, with a likely range reaching well above 4 degrees—often viewed as a rough threshold for a complete collapse of the climate system.
There are two lower-emissions scenarios in the report, the lowest of which keeps the temperature rise by the century’s end under 1.5 degrees (after exceeding it briefly), but a quick analysis from MIT’s Technology Review points out that this scenario relies mainly on highly speculative “negative emissions” technologies, especially carbon capture and storage, and a shift toward the massive-scale use of biomass (i.e. crops and trees) for energy. We know that a more widespread use of “energy crops” would consume vast areas of the earth’s landmass, and that the regrowing of trees that are cut down to burn for energy would take many decades to absorb the initial carbon release—a scenario the earth clearly cannot afford. The lower-emissions scenarios also accept the prevailing rhetoric of “net-zero,” assuming that more widespread carbon-sequestering methods like protecting forests can serve to compensate for still-rising emissions. We know that many if not most carbon offset schemes to date have been an absolute failure, with Indigenous peoples often driven from their traditional lands in the name of “forest protection,” only to see rates of commercial logging increase rapidly in immediately surrounding areas.
It is increasingly doubtful that genuine long-term climate solutions can be found without a thorough transformation of social and economic systems. It is true that the cost of renewable energy has fallen dramatically in the past decade, which is a good thing, and that leading auto manufacturers are aiming to switch to electric vehicle production over the coming decade. But commercial investments in renewable energy have leveled off over the same time period, especially in the richer countries, and continue to favor only the largest-scale projects that begin to meet capitalist standards of profitability. Fossil fuel production has, of course, led to exaggerated standards of profitability in the energy sector over more than 150 years, and most renewable projects fall far short. We will likely see more solar and wind power, a faster tightening of fuel efficiency standards for the auto industry and subsidies for electric charging stations in the US, but nothing like the massive reinvestment in community-scaled renewables and public transportation that is needed. Not even the landmark Biden-Sanders budget reconciliation plan that is under consideration in in the US Congress, with all its necessary and helpful climate measures, addresses the full magnitude of changes that are needed to halt emissions by midcentury. While some obstructionists in Congress appear to be stepping back from the overt climate denial that has increasingly driven Republican politics in recent years, they have not backed away from claims that it is economically unacceptable to end climate-altering pollution.
Internationally, the current debate over reducing carbon pollution (so called “climate mitigation”) also falls far short of addressing the full magnitude of the problem, and generally evades the question of who is mainly responsible. While the US and other wealthy countries have produced an overwhelming share of historic carbon pollution since the dawn of the industrial era, there is an added dimension to the problem that is most often overlooked, and which I reviewed in some detail in my Introduction to a recent book (co-edited with Tamra Gilbertson), Climate Justice and Community Renewal (Routledge 2020). A 2015 study from Thomas Piketty’s research group in Paris revealed that inequalities within countries have risen to account for half of the global distribution of greenhouse gas emissions, and several other studies confirm this.
Researchers at Oxfam have been studying this issue for some years, and their most recent report concluded that the wealthiest ten percent of the global population are responsible for 49 percent of individual emissions. The richest one percent emits 175 times more carbon per person on average than the poorest ten percent. Another pair of independent research groups have released periodic Carbon Majors Reports and interactive graphics profiling around a hundred global companies that are specifically responsible for almost two-thirds of all greenhouse gases since the mid-19th century, including just fifty companies—both private and state-owned ones—that are responsible for half of all today’s industrial emissions (See climateaccountability.org). So while the world’s most vulnerable peoples are disproportionately impacted by droughts, floods, violent storms and rising sea levels, the responsibility falls squarely upon the world’s wealthiest.
When the current IPCC report was first released, the UN Secretary General described it as a “code red for humanity,” and called for decisive action. Greta Thunberg described it as a “wake-up call,” and urged listeners to hold the people in power accountable. Whether that can happen quickly enough to stave off some of the worst consequences will be a function of the strength of our social movements, and also our willingness to address the full scope of social transformations that are now essential for humanity and all of life on earth to continue to thrive.