The research underscores the challenges nations face as climate projections become grimmer, and the odds of limiting global warming to an acceptable level shrink.
In the first study, researchers used statistical tools to determine the likelihood of different levels of warming. The report gives a 1 percent chance that average temperatures on Earth will be at or below 2.7 degrees Fahrenheit above pre-industrial levels by the end of the century: the primary goal of the 2016 Paris agreement. President Donald Trump announced in June that he was withdrawing the United States from the treaty.
“Our analysis is compatible with previous estimates, but it finds that the most optimistic projections are unlikely to happen,” said lead author Adrian Raftery, a professor at the University of Washington. “We’re closer to the margin than we think.”
Warming beyond 3.6 degrees Fahrenheit, or 2 degrees Celsius, is viewed as the “tipping point” at which the side effects of climate change become more extreme. The research shows a 5 percent chance that global warming will be at or below that level by the end of this century.
“Our analysis shows that the goal of 2 degrees (Celsius) is very much a best-case scenario,” Raftery said. “It is achievable, but only with major, sustained effort on all fronts over the next 80 years.”
In the second study, researchers found that even if all greenhouse gas emissions instantly stopped, Earth would continue to heat up about another 2 degrees Fahrenheit by the end of the century. If current emission levels continue for 15 years, the planet would likely experience nearly 3 degrees Fahrenheit of warming by 2100.
One degree Celsius, or Centigrade, is equal to 1.8 degrees Fahrenheit.
“This ‘committed warming’ is critical to understand because it can tell us and policy makers how long we have, at current emission rates, before the planet will warm to certain thresholds,” said co-author Robert Pincus, a scientist at the University of Colorado, Boulder and the National Oceanic and Atmospheric Administration. “The window of opportunity on a 1.5-degree [C] target is closing.”
The team’s analysis relies on observations of the climate system to calculate Earth’s committed warming, compared with computer simulations. The research accounts for the climate-relevant behavior of fine participles in the atmosphere, the ocean’s capacity to absorb carbon, data on the planet’s energy imbalance, and other factors.
The study shows a 13 percent chance that Earth is already bound to warm up 2.7 degrees Fahrenheit by 2100. If all greenhouse gas emissions stop in 2017, the team projects warming by 2100 to be between 1.6 and 4.1 degrees Fahrenheit, though the ocean could reduce committed warming by 0.4 degrees Fahrenheit.
“Our estimates are based on things that have already happened, things we can observe, and they point to the part of future warming that is already committed to by past emissions,” said lead author Thorsten Mauritsen, from the Max Planck Institute for Meteorology. “Future carbon dioxide emissions will then add extra warming on top of that commitment.”
The impact of climate change on human health also will increase, and is expected to cause about 60,000 deaths globally in 2030 and 260,000 deaths in 2100 due to increasing air pollution, according to the third study.
Led by scientists from the University of North Carolina at Chapel Hill, the research uses results from several of the leading climate change modeling groups to estimate the number of premature deaths that would stem from particulate matter and ozone in 2030 and 2100.
“As climate change affects air pollutant concentrations, it can have a significant impact on health worldwide, adding to the millions of people who die from air pollution each year,” said lead author Jason West, an associate professor at UNC-Chapel Hill.
Warmer temperatures accelerate chemical reactions that create air pollutants such as ozone and fine particulate matter, which affect public health. Drier areas are especially affected due to less pollutant removal by rain, increased fires and windblown dust.
The team found that global warming is expected to increase air pollution-related deaths globally, except in Africa. Five out of eight models forecast there will be more premature deaths in 2030, while seven of nine models predicted additional deaths in 2100.
“Our finding that most models show a likely increase in deaths is the clearest signal yet that climate change will be detrimental to air quality and health,” West said.