Much has been made of the various promises to cut back on carbon emissions by national leaders. The stated goal was to limit temperature rise at the end of this century to less than 2.0 degrees C (3.6 degrees F), and preferably to less than 1.5 degrees C. The Economist paper led a recent issue with an assessment of the probabilities that those goals could be met: What’s the worst that could happen. The lede provided this conclusion.
“Three degrees of global warming is quite plausible and truly disastrous”
It seems meeting the targets is not a given.
“Those Paris targets were, and remain, both prudent and incredibly ambitious. Right after the conference Climate Action Tracker (CAT), an NGO, set itself the task of totting up all the emission-reduction goals and other policies, like fuel-efficiency standards for cars and trucks and renewable-energy targets, that the various nations had made. To gauge the aggregate impact of those measures, cat calculated the atmospheric concentrations of carbon dioxide they looked likely to produce and then used the results of climate models to see what those concentrations might mean in terms of warming. Their results showed the world was on track to be 2.7°C hotter than the pre-industrial baseline by 2100.”
Clearly, bigger and better promises were called for.
“Revised pledges formally submitted to the un over the past 12 months in the run-up to the COP26 conference to be held in November have knocked CAT’s estimate down a bit. If all government promises and targets are met, warming could be kept down to 2.4°C. Including targets that have been publicly announced but not yet formally entered into the Paris agreement’s ledgers, such as America’s net-zero-by-2050 pledge and China’s promise to be carbon-neutral by 2060, brings the number down to a tantalising 2.0°C.”
As often, making an estimate based on actions that are actually taking place can be a better strategy.
“A world which follows the policies that are actually in place right now would end up at 2.9°C, according to CAT (the UN Environment Programme, which tracks the gap between actual emissions and those that would deliver Paris, provides a somewhat higher estimate). Almost everyone expects or hopes that policies will tighten up at least somewhat. But any reasonable assessment of the future has to look at what may happen if they do not.”
The article goes on to discuss the consequences of reaching a global temperature 3.0 degrees warmer than the baseline and concludes that they are “truly disastrous.” A problem with this approach is that every time the scientists agree on a climate model projection, they have been too conservative. What the article describes is likely more benign than what reaching plus 3 degrees C will likely unleash. Mark Lynas is a journalist who has spent many years tracking the latest research and modeling in the area of climate change and global warming. He described his perception of what could happen in his book OurFinal Warning: Six Degrees of Climate Emergency.
The Economist concludes a discussion of the threats a plus 3 degree C world’s food supply faces with this observation.
“Although the Intergovernmental Panel on Climate Change (IPCC) estimates that cereal prices might be 29% higher under 3°C of warming, putting 183m people at additional risk of hunger, it also sees it as possible that they might hardly shift at all.”
Lynas provides a different take.
“In the three-degree world, therefore, we face drastic harvest losses at the same time that the global human population is projected to rise to 10 billion. To feed these extra mouths, and to do so at the same time as reducing poverty, requires doubling food production globally by mid-century. Instead, in a three-degree scenario we could see food production cut by half.”
Lynas seems to make the more convincing argument. For more on the food issue, check out Growing Food in a Warming Climate.
Lynas’s frustration with the timidity of the official proclamations that emerge from science-by-committee occasionally boil over.
“When I started writing this book I thought that we could probably survive climate change. Now I am not so sure…we are already living in a world one degree warmer than that inhabited by our parents and grandparents. Two degrees Celsius, which will stress human societies and destroy many natural ecosystems such as rainforests and coral reefs, looms on the near horizon. At three degrees I now believe that the stability of human civilization will be seriously imperiled, while at four degrees a full-scale global collapse of human societies is probable, accompanied by a mass extinction of the biosphere that will be the worst on Earth for tens or even hundreds of million years. By five degrees we will see massive positive feedbacks coming into play, driving further warming and climate impacts so extreme that they will leave most of the globe biologically uninhabitable, with humans reduced to a precarious existence in small refuges. At six degrees we risk triggering a runaway warming process that could render the biosphere completely extinct and forever destroy the capacity of this planet to support life.”
Consider his potential timeline for a business-as-usual approach to limiting climate change.
“If we stay on the current business-as-usual trajectory, we could see two degrees as soon as the early 2030s, three degrees around mid-century, and four degrees by 2075 or so. If we’re unlucky with positive feedbacks,,,from thawing permafrost in the artic or collapsing tropical rainforests, then we could be in for five or even six degrees by the century’s end.”
George Keeling is the scientist who began measuring the CO2 concentration and demonstrating its seemingly inexorable growth. Its time-dependence is referred to as the Keeling Curve. For Lynas this data illustrates the ineffectiveness of humanity’s paltry efforts and sets the stage for what is to come.
“…the rate of CO2 accumulation in the atmosphere is steadily increasing, from roughly 1 ppm [parts per million] in the early years to about 2 ppm annually today. There is no visible slowdown, no sudden downwards blip, to mark the implementation of the Kyoto Protocol, still less 2009’s Copenhagen ‘two degrees’ commitment or the landmark Paris Agreement of 2015. All those smiling heads of state shaking hands, the diplomats hugging on the podium after marathon sessions of all-night negotiating—none of that actually made any identifiable difference to the Keeling Curve, which is the only thing that actually matters to the planet’s temperature. All our solar panels, wind turbines, electric cars, lithium-ion batteries, LED lightbulbs, nuclear plants, biogas digesters, press conferences, declarations, pieces of paper; all our shouting and arguing, weeping and marching, reporting and ignoring, decrying and denying; all our speeches, movies, websites, lectures and books; our announcements, carbon-neutral targets, moments of joy and despair; none of these to date have so much as made the slightest dent in the steepening upward slope of the Keeling Curve.”
If the CO2 level is “the only thing that actually matters to the planet’s temperature, a comparison of historical levels of CO2 and estimates of the Earth’s average temperature should be informative. A Wikipedia article provides those charts.
As of 2019, the concentration of CO2 in the atmosphere was 409.8 parts per million (ppm).
Glen Fergus provides historical estimates of the Earth’s temperature.
Comparing the two curves, particularly during the Pleistocene with its recurring ice ages, suggests a close but not perfect correlation between Earth average temperature and CO2 concentration. Temperatures in the plus 2-3 degrees C range could be reached in the interglacial stages. The last of these warm periods is known as the Eemian. It lasted about 15,000 years and its characteristic temperature was in the plus 1-2 degrees C range, not much different than where we are today. In that warm period, it created a much different world than what we see now: sea level was 20-30 feet higher than today, forests extended well above the Arctic Circle, and hippopotamuses were frolicking in the Rhine and Thames Rivers. These changes were obtained with a CO2 concentration of about 280 ppm and the allowance of a little time for plants and animals to follow the climate changes.
We have relentlessly blown past the Eemian CO2
concentration, much faster than the temperature can follow. But it will catch up and the world will be
transformed. The changes may not come as
fast as Lynas fears, but we have disrupted the world in which our civilization
developed, and it will never be the same again.
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