This month, we learned that we have just lived through the hottest year on the planet since the mid-19th century, when good records began. For almost half of 2023, Earth’s temperature was 1.5 C above the benchmark average temperature for 1850-1900. Additional estimates suggest that 2023 may have been the hottest year in 100,000 years. The atmospheric concentrations of both carbon dioxide (419 ppm) and methane (1902 ppb) were also at record levels, 50% and 163%, respectively, above concentrations from before the industrial revolution. That was all expected news, but bad news nonetheless. How should we mentally process and act on it?
In light of the incremental progress of global climate negotiations at last month’s U.N. Climate Conference (COP28) and this latest evidence of warming, a leader of a major climate-focused foundation told me, “I am a short-term pessimist and a long-term optimist.” That also describes my quantitative assessment and emotional response to climate change.
First, the short-term pessimism.
For the rest of my life, my children’s lives, and probably for the lives of my toddler grandchildren, we can expect every year to be the hottest year on record. There will be exceptions, but the upward trend is unlikely to change for another couple of generations. If my grandchildren achieve close to the current average U.S. life expectancy of 78 years, the planet’s average temperature will likely have risen at least 2.5 C, and probably much more, above that benchmark by the end of their lives. Even if GHG emissions ended tomorrow, global temperatures would remain elevated for hundreds of years. We should stop being distracted by the recurrent breaking of the hottest year record.
Of more existential concern are the impacts of rising global temperatures, and what they portend for society. The indisputable direct impacts include more severe natural disasters, increased food insecurity, and accelerated human migration. Indirect effects are less amenable to prediction, but are highly likely to include increased wealth inequality and political instability, the rise of more populists and autocrats, and, ultimately, armed conflict. These direct and indirect shocks to social and political systems increase human suffering, especially by those already on the economic edge (and water’s edge). Such changes could directly threaten my grandchildren’s lives and the lives of countless others.
If climate change is accelerating, which the most recent data for both atmosphere and oceans suggest, and if feedback loops grow stronger, the possibility exists for runaway warming and disasters beyond our current imaginations. As the atmosphere and seas warm, sea ice and glaciers melt, increasing the absorption of solar radiation on sea and land, which in turn accelerates warming, melting, sea level rise, and the cycle spins again. Such vicious cycles would undermine efforts to slow climate change and would make social instability even more likely.
Hence it is easy to understand climate change-induced despair, cynicism, ecoanxiety, and loss of hope. However, Martin Luther, the 16th century church reformer, is reputed to have said, “If I knew tomorrow was the end of the world, I would plant an apple tree today.” That expression of hope is now more appropriate than ever (and includes a meaning Luther could not have considered: the role of trees as carbon sinks!).
Second, the long-term optimism.
Public support for climate action continues to increase everywhere. In the US, 72% of adults now believe global warming is real, 58% believe it is caused by humans, and 54% believe the president should do more to address global warming, according to 2023 polling by the Yale Program on Climate Communication.
The climate research and policy communities are getting more realistic. For decades, there was peer pressure to limit our climate change response toolbox to one tool: mitigation (preventing emissions). Thirty years ago, most leading environmental groups refused to talk about adaptation (changing our behavior and infrastructure in response to changes we have not prevented), because they viewed it as a dangerous distraction. In 1992, Al Gore blasted consideration of adaptation as “laziness.” Fifteen years later, Gore had recanted, and adaptation was firmly on the U.N. agenda. In another step in the right direction, the climate science community is finally accepting geoengineering (large-scale intervention in the climate system to reverse climate change or its symptoms) as another potential response tool.
By blowing past the 1.5 C target – and we most surely will – we may lose a motivating target number. But 1.5 C had garnered an almost magical aura, and the loss of it will help us move beyond magical thinking about solutions. Specifically, I am optimistic that this inflection will shift our silver-bullet thinking to a more explicitly silver-buckshot approach encompassing the full set of potential tools: mitigation, adaptation, and geoengineering.
Now that adaptation and geoengineering are out of the academic shadows and can contribute to an all-of-the-above approach to climate action, we need to devote to them the kind of deep research, serious policy analysis, and public and private investment previously focused solely on mitigation. If we can act fast, the argument for long-term optimism on all three fronts is strong, and, I believe, even stronger if government policies see all three approaches as essential and complementary, and incentivize private action accordingly.
Every bit of progress matters, using all the tools available.
For mitigation, economic reality and policy-driven innovation and incentives are slowing emissions via the phase out of coal, increased deployment of renewable energy, market penetration by EVs, and most recently, mandated reductions in methane leakage. Aspirations and policies on emissions reductions have been strengthened, and progress is especially strong as measured per unit of economic output. More essential for the long-term, total emissions are declining in some nations. In 2023, U.S. emission of GHG emissions declined 1.9% even as the economy expanded over 2.4%. Further acceleration of these trends in the U.S. is happening via efforts to streamline the permitting process for large solar and wind farms, and the grid connections essential to them, and to build a much larger network of reliable EV chargers to increase consumer acceptance.
With increases in the contributions of cash and technical assistance from the Global North to the Global South, including from the new U.N. Loss and Damage Fund, billions of people could be lifted out of poverty with renewable energy sources.
Adaptation tactics are much more diverse and context dependent than mitigation tactics, but they are often motivated by citizens with obvious risks from climate change. Adaptation is now widely practiced in red and blue U.S. states and across the planet. Coastal towns in Alaska and Louisiana are being relocated away from flood risk. Climate smart farming practices are being employed and different crops are being grown in response to changed climate. In Miami, numerous streets have been raised to avoid sunny day flooding; private and public insurance rate increases are steering people away from living in flood- and fire-prone areas; and billions of private and public dollars are being spent to reduce heat stress on employees and citizens, including planting trees to reduce urban heat islands and reduce climate injustice. Western U.S. states dependent on Colorado River water are renegotiating how to share the dwindling river flow. In the U.S., greater private and public investments at city, state, and national scales will increase the pace of adaptation, while the U.N. Global Adaptation Fund is fueling similar changes in the Global South.
Geoengineering, the most immature tool, is the only one capable of reversing climate change. It includes carbon dioxide removal, which is currently growing with government incentives in the U.S. and elsewhere, and solar radiation management, which remains very exploratory.
Carbon dioxide removal is accomplished via carbon capture (by plants or chemical processes), with the carbon sometimes sequestrated underground or in long-lasting products (e.g., concrete), or used as a fuel source (e.g., ethanol from corn). Bioenergy with Carbon Capture and Storage (BECCS) has been a mainstay of U.N. integrated assessment models for almost 15 years. Other carbon capture approaches include additions of biochar and rock dust to soil, both of which have the potential to sequester carbon while improving agricultural productivity. Overall carbon dioxide removal’s promise remains uncertain given many technical unknowns, its reversibility for soils and plants (think forest fires), potential competition for land between carbon capture and food production, and the currently very high cost of engineered approaches to carbon capture. Greater investments in research and development, and subsequent rigorous analyses of costs and outcomes, are necessary to sort out which approaches can cost effectively contribute to reducing atmospheric carbon dioxide at the scales required.
The most potentially consequential geoengineering approach is solar radiation management via injection of particles into the stratosphere to reflect the sun’s energy back into space. This would be akin to what the most explosive volcanic eruptions have done in the past. Solar radiation management would not affect the underlying cause of climate change (the concentration of GHGs in the atmosphere). Thus many symptoms of climate change, including ocean acidification, would be unaffected. Rather, solar radiation management would directly affect only one, albeit very important, aspect of climate change – Earth’s temperature (and the many indirect effects of temperature). Given the potential for temperature driven vicious feedback loops of accelerating climate change, solar radiation management could be a stopgap mechanism to greatly reduce human suffering while economic development continues in the Global South, and mitigation and adaptation everywhere catch up. To have a sufficient understanding of the potential benefits and risks of solar radiation management, the U.S. and other countries need a much better funded research program that includes technical, social, and governance aspects of potential deployment.
My long-term optimism is thus based on the expectation that synergism among government policies, innovation in research, and increasing mobilization of public-private partnerships will lead to accelerating deployment of adaptation and geoengineering. Along with increased mitigation, this diverse toolbox will slow, halt, and eventually reverse climate change. As part of this all-of-the-above strategy, a judicious and temporary application of solar radiation management, if further research suggests the balance of benefits and risks warrants it, could even prove false my prediction of the temperatures future generations including my grandchildren will endure. I would be grateful to be wrong.
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