SUMMIT COUNTY — Scientists with the Scripps Institution of Oceanography have outlined a three-pronged approach to avoid reaching a critical global warming threshold that could lead to “unmanageable climate change.”
The recommended steps include stabilizing atmospheric carbon dioxide, adopting warming neutral pollution control laws and reductions of short-lived greenhouse gases that are nevertheless highly potent, including methane and hydrofluorocarbons.
Avoiding the threshold requires keeping carbon dioxide levels below 441 parts per million, according to the authors, only slightly higher than today’s value of 389 ppm. This equates to a 50 percent reduction in greenhouse gas emissions by 2050 and an 80 percent reduction by 2100.
This drastic reduction will require a “portfolio of actions in the energy, industrial, agricultural and forestry sections … new technologies and a massive decarbonization of the energy sector,” climate researchers Veerabhadran Ramanathan and Yangyang Xu wrote in a paper published May 3 in the Proceedings of the National Academy of Sciences.
The scientists said aggressive, simultaneous pursuit of these strategies could reduce the probability of reaching the temperature threshold to less than 10 percent before the year 2050. The best available science suggests that exceeding the temperature threshold would trigger irreversible phenomena such as widespread release of methane from melting permafrost and large-scale glacial melt, both of which scenarios would exacerbate climate change-related problems such as sea-level rise and acceleration of global warming.
“Without an integrated approach that combines CO2 emission reductions with reductions in other climate warmers and climate-neutral air-pollution laws, we are certain to pass the 2-degree Celsius and likely reach a 4 degree Celsius threshold during this century,” said Scripps climate researcher Veerabhadran Ramanathan. “Fortunately there is still time to avert unmanageable climate changes, but we must act now.”
The conclusions follow on the December Copenhagen agreement by major greenhouse gas-emitting countries to try and prevent global temperatures from climbing more than 2 degrees Celsius (3.6 degrees Fahrenheit).
Complicating the equation is the fact that reductions in pollution will also result in fewer emissions of certain types of aerosols that actually cool the atmosphere by reflecting sunlight rather than absorbing it. The aerosols are a wild card in the scenario, Ramanathan and co-author Yangyang Xu acknowledge, suggesting demonstration projects to prove the effectiveness of mitigation strategies.
Oceans could be one early proving ground, they said, explaining that oceans would respond to mitigation actions even before 2050, making them an important diagnostic tool that can gauge the success of mitigation within 20 years.
Outside of the drastic changes required in the energy, agriculture and forestry sectors, other strategies for avoiding the temperature threshold can take advantage of existing technologies and more aggressive enforcement of existing regulations. That includes replacement of biomass-fueled stoves with cleaner alternatives in developing countries and retrofitting of diesel filters on vehicles throughout the world in a “low-hanging fruit” approach that cleans up the environment, protects human health and helps to avoid the 2-degree threshold.
The authors also pointed out that the world has already succeeded before in removing dangerous warming agents. The 1987 Montreal Protocol regulated the use of chlorofluorocarbons, helping to limit the damaging effect of the chemicals on the planet’s ozone layer. Without that ban, temperatures would be climbing even more drastically than they are today.