While the climate policy world is littered with numbers, three of them have dominated recent discourse: 2, 1000, and 66.



At the 2015 U.N. climate summit in Paris, world leaders agreed to limit global warming below 2°C to avoid catastrophic impacts of human-caused climate change. The science consequently dictates that, for a 50% chance of staying below 2°C, around 1,000 billion tonnes of carbon dioxide (or 300 billion tonnes of carbon) can be emitted between now and 2050, and close to zero thereafter. We’re currently emitting 36 billion tonnes of carbon dioxide per year. However, the potential greenhouse gas emissions contained in known, extractable fossil fuel reserves are around three times higher than this carbon budget, meaning that 66% must be kept in the ground.

The debate du jour thus centers on which emissions reduction pathway is most optimal for staying below 2°C. The calculus of many policymakers, economists, fossil fuel companies, and indeed scientists, is that the most economical way to stay below 2°C is to delay most emissions reductions for decades to come, and then to play catch up by relying heavily on as-yet technically and economically unviable negative-emissions technologies. However, a crucial number has been neglected in this mainstream calculation: 6.1 million.

Each year, 6.1 million lives are lost prematurely due to air pollution. Though most acutely and visibly hampering megacities of the developing world, air pollution is a growing public health emergency that affects almost all of us in our daily lives, whether or not we are aware of it. The Health Effects Institute estimates that only 5% of the global population are lucky enough to live in areas with air pollution levels below safe guidelines. Though recent studies suggest there may in fact be no risk-free level of air pollution.

Why is this number relevant to climate policy? Because one common culprit is responsible for the majority of both climate change and air pollution: fuel combustion. Burning coal, oil, natural gas, and biomass – for everyday uses ranging from electricity, heating, cooking, to transportation – releases hundreds of gases and particles, some of which disrupt the climate system or are harmful to human health, or both. Climate change could also worsen air quality in the future.

Decades of research have revealed that air pollution is associated with a wide range of diseases and disorders, including asthma, cancer, heart disease, stroke, and premature birth. There is also emerging evidence that pollution from coal combustion and motor vehicles can cause development delays, reduced IQ, and autism in children. The societal and economic costs of air pollution are multifold. There are costs to the affected individuals, to their families and to society in terms of direct medical costs, costs to healthcare systems, productivity losses, and lower economic growth (not to mention costs resulting from damages to ecosystems).

Yet almost none of these costs stemming from our fossil fuel reliance are included in the majority of cost-benefit analyses of climate mitigation strategies. A recent study estimates that the health co-benefits from air pollution reductions would outweigh the mitigation costs of staying below 2°C by 140–250% globally. Historical evidence paints a similar picture. The EPA estimates that the U.S. Clean Air Amendments cost $65bn to implement, but will have yielded a benefit of almost $2tn by 2020 in avoided health costs.

Many public health expert groups have underscored the enormous opportunity for leaders worldwide to design policies and initiatives that will simultaneously tackle climate change and air pollution. Examples include replacing the most carbon-intensive and polluting sources such as coal and heavy-duty diesel with lower-emission or renewable alternatives, ending fossil fuel subsidies, redesigning urban spaces to make it easier and safer to commute by foot, bicycle, and public transportation, and transitioning to a more circular and sustainable economy. While the climatic mitigation effects of such measures are long-term and dispersed globally, the health benefits are immediate and local.



For too long, the enormous toll of disease and deaths from fossil fuel pollution has been neglected in climate change policies and underappreciated by the public. But public health data makes it clear that not all 2°C scenarios are created equal. The lives and well-being of hundreds of millions of us – especially our children – could be at stake. We would be remiss to ignore it.

Dr. Ploy Achakulwisut is a Postdoctoral Scientist at the George Washington University Milken Institute School of Public Health. She has a PhD in Atmospheric Science from Harvard University.