This came up in the comments on my post about the Arctic heat wave, and I think it merits further discussion.
Even ignoring the multiple feedback loops that are likely to see the planet’s warming continue long into the future, if we do everything right in terms of addressing climate change there will be severe warming in our lifetimes. This is not a new concern. Aerosol pollution played a role in the cooling period of the 1970s that climate deniers love to talk about, and after the environmental movement of that era succeeded in reducing air pollution, there was an increase in temperature that followed.
This is one of the reasons I consistently advocate for climate action that includes taking dramatic steps to prepare for a much warmer and more unpredictable world. If we had taken serious action to reduce energy consumption, develop renewable energy, and expand and improve nuclear energy in the 1970s and 1980s, we would have different options available to us today, but we missed that window. Returning to the “pre-industrial norm”, within our lifetimes, no longer seems to be an option. As I discussed in my geoengineering post, we have to learn how to responsibly use the collective power we’ve developed as a species if we want a livable world for future generations.
The effect was first spotted by Gerry Stanhill, an English scientist working in Israel. Comparing Israeli sunlight records from the 1950s with current ones, Stanhill was astonished to find a large fall in solar radiation. “There was a staggering 22% drop in the sunlight, and that really amazed me,” he says.
Intrigued, he searched out records from all around the world, and found the same story almost everywhere he looked, with sunlight falling by 10% over the USA, nearly 30% in parts of the former Soviet Union, and even by 16% in parts of the British Isles. Although the effect varied greatly from place to place, overall the decline amounted to 1-2% globally per decade between the 1950s and the 1990s.
Gerry called the phenomenon global dimming, but his research, published in 2001, met with a sceptical response from other scientists. It was only recently, when his conclusions were confirmed by Australian scientists using a completely different method to estimate solar radiation, that climate scientists at last woke up to the reality of global dimming.
Dimming appears to be caused by air pollution. Burning coal, oil and wood, whether in cars, power stations or cooking fires, produces not only invisible carbon dioxide (the principal greenhouse gas responsible for global warming) but also tiny airborne particles of soot, ash, sulphur compounds and other pollutants.
This visible air pollution reflects sunlight back into space, preventing it reaching the surface. But the pollution also changes the optical properties of clouds. Because the particles seed the formation of water droplets, polluted clouds contain a larger number of droplets than unpolluted clouds. Recent research shows that this makes them more reflective than they would otherwise be, again reflecting the Sun’s rays back into space.
Reducing CO2 emissions means reducing the production of these other forms of pollution. The global shutdown triggered by the COVID-19 pandemic showed us how dramatically a decrease in fossil fuel use can clear the air of visible pollution, and this will doubtless provide climate scientists with a wealth of data on what we can expect from the kind of rapid, permanent drop in fossil fuel use. Research published in 2019 indicated that climate scientists have been under-estimating the cooling effect of aerosol pollution:
To what extent do aerosols cool down our environment? To date, all estimates were unreliable because it was impossible to separate the effects of rising winds which create the clouds, from the effects of aerosols which determine their composition. Until now.
Rosenfeld and his colleague Yannian Zhu from the Meteorological Institute of Shaanxi Province in China developed a new method that uses satellite images to separately calculate the effect of vertical winds and aerosol cloud droplet numbers. They applied this methodology to low-lying cloud cover above the world’s oceans between the Equator and 40S. With this new method, Rosenfeld and his colleagues were able to more accurately calculate aerosols’ cooling effects on the Earth’s energy budget. And, they discovered that aerosols’ cooling effect is nearly twice higher than previously thought.
However, if this is true then how come the earth is getting warmer, not cooler? For all of the global attention on climate warming, aerosol pollution rates from vehicles, agriculture and power plants is still very high. For Rosenfeld, this discrepancy might point to an ever deeper and more troubling reality. “If the aerosols indeed cause a greater cooling effect than previously estimated, then the warming effect of the greenhouse gases has also been larger than we thought, enabling greenhouse gas emissions to overcome the cooling effect of aerosols and points to a greater amount of global warming than we previously thought,” he shared.
The fact that our planet is getting warmer even though aerosols are cooling it down at higher rates than previously thought brings us to a Catch-22 situation: Global efforts to improve air quality by developing cleaner fuels and burning less coal could end up harming our planet by reducing the number of aerosols in the atmosphere, and by doing so, diminishing aerosols’ cooling ability to offset global warming.
According to Rosenfeld, another hypothesis to explain why Earth is getting warmer even though aerosols have been cooling it down at an even a greater rate is a possible warming effect of aerosols when they lodge in deep clouds, meaning those 10 kilometers or more above the Earth. Israel’s Space Agency and France’s National Centre for Space Studies (CNES) have teamed up to develop new satellites that will be able to investigate this deep cloud phenomenon, with Professor Rosenfeld as its principal investigator.
Either way, the conclusion is the same. Our current global climate predictions do not correctly take into account the significant effects of aerosols on clouds on Earth’s overall energy balance. Further, Rosenfeld’s recalculations mean fellow scientists will have to rethink their global warming predictions — which currently predict a 1.5 to 4.5-degree Celsius temperature increase by the end of the 21st century — to provide us a more accurate diagnosis — and prognosis — of the Earth’s climate.
An erratum published a couple months later indicated that the degree of mis-calculation may not be as severe as Rosenfeld et al. initially stated, but their overall conclusion remains intact. The overall message remains the same as it has been – the problem of global warming has not been addressed in a manner that allows us to avoid serious consequences this century. That means an unprecedented refugee crisis, crop failures, heat waves, wildfires, and increasingly severe coastal flooding. These are all crises we are capable of dealing with. We have the technology and the understanding to help refugees, relocate or re-design coastal cities, and mage huge changes to global food production.
What we don’t have, currently, is a political and economic system that allows us to respond to the demands of our time. We cannot afford to have global production, distribution, and human movement to be dictated by and for the benefit of a tiny fraction of humanity. The drive for endless growth, and endless capital accumulation, even if we did have a more progressive system of taxation and wealth re-distribution, creates artificial scarcity, and prevents the development of a society that can be sustained in the long term.
This is not just an emergency created by our use of energy, it’s also rooted in the capitalist system that currently governs nearly all human activity on this planet. We need radical democracy in politics and in economies if we’re to have any hope of addressing our environmental crisis, and of saving humanity. We need it soon.
Unfortunately, life costs money, and my income from this blog has yet to meet minimum wage for the time I put into it. If you can afford to, please consider pledging a couple dollars per month or so through my Patreon. This will help me continue creating and improving this blog by keeping a roof over my head, and food in my carnivorous pets so they don’t eat me. Crowdfunding requires a crowd, so if you can pitch in a little, it would help a great deal!