Flavio Lehner

Climate scientist and assistant professor of earth and atmospheric science

Flavio Lehner, a climate scientist and assistant professor of earth and atmospheric science at Cornell University, studies ways to improve climate change projections. Lehner says human-caused environmental problems have historically been solved by government regulations affecting markets and that the anticipated U.S. commitment will drive regulatory and tech innovations and spark energy transitions.

Lehner says:

“A more ambitious emissions target by the U.S. is welcome from several perspectives. First, reducing emissions is still the sole viable solution to stabilizing the climate, due to the inherent cumulative nature of CO2 concentrations in the atmosphere. The longer one waits, the harder it is to reverse. Second, the U.S. can (re-)take a leadership role in stabilizing the climate. They have the political and monetary capital to drive both regulatory and technological innovation. Third, providing incentives and regulations will ensure a faster and more equitable energy transition. Virtually all large historical human-caused environmental problems were solved not by the free market, but by the market responding efficiently to government regulations and incentives. The same is likely true for greenhouse gas emissions.

“Is the new pledge realistic? It is very ambitious, even if one considers that U.S. greenhouse gas emissions have actually been declining already since 2007. The COVID crisis has further reduced emissions, but they are poised to rebound to some extent. Strategic post-COVID investments in infrastructure provide a unique opportunity to accelerate decarbonization, but cautious skepticism regarding the realism of the new U.S. target is nonetheless warranted.

“Is this new pledge enough? Probably not, but this also depends on what other major emitters will do this decade. It is certainly not enough to reach the 1.5°C target, as this would require sustained COVID-like global emission reductions (~7% per year). Even reaching 2°C remains unrealistic given current pledges by the major emitters. However, these warming targets are aspirational. Conditions will simply continue to worsen as the climate warms, but there are no known catastrophic climate tipping points at exactly 1.5°C or 2°C warming. Certain low-lying island nations, however, will be critically endangered by sea level rise as projected to occur if the climate stabilizes at a level above 1.5°C. It is well-understood that many climate impacts scale almost linearly with warming, so reducing emissions as fast as possible has to remain a key sustained motivation for this and future administrations, irrespective of a particular warming target.”