How much warming can the world bear?
That question is one of the fundamental issues in dispute at the ongoing U.N. climate change summit, known as COP26, in Glasgow, Scotland.
Here’s what different levels of warming would look like, and how global temperature targets have been set.
Six years ago, when countries came together in Paris for the COP21 summit, at which the Paris climate accord was shaped, they committed to limit the global average temperature rise to well below 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels.
However, while the 2015 agreement set 2C as the minimum, it included language that suggested countries should push for a more ambitious goal: 1.5C.
A preliminary draft of the COP26 agreement released Wednesday “reaffirms” the Paris agreement’s goal: limiting warming to well below 2C and pursuing a target of 1.5C. But it does not commit to meeting the 1.5C threshold.
The difference between the two targets may seem small, but they represent vastly different levels of effort for countries seeking to limit their carbon footprints, and strikingly divergent outcomes for the planet.
Some experts doubt that 1.5C remains achievable. Limiting warming to 1.5C “will be very difficult,” Microsoft founder and philanthropist Bill Gates told U.K. lawmaker Jeremy Hunt in a conversation hosted by the think tank Policy Exchange last week.
Evidence shows that the two targets also represent different scenarios for the climate’s impact on human life.
A study released Tuesday by the U.K. Met Office, Britain’s national weather service, found that 1 billion people could face heat stress, a potentially fatal combination of heat and humidity, if temperatures rise by 2C.
“The higher the level of warming, the more severe and widespread the risks to people’s lives, but it is still possible to avoid these higher risks if we act now,” said Richard Betts, one of the leaders of the project.
Tuvalu's foreign minister gave a speech to COP26 on Nov. 8, standing in the ocean to show how his Pacific island nation is on the front line of climate change. (Reuters)
How did the world agree upon a 2C target?
When world leaders came together in Paris in 2015, they were looking to reverse a long period of international inaction after the widely perceived failures of the 1992 Kyoto Protocol and the 2009 Copenhagen Accord.
The latter had included nonbinding language that referenced “the scientific view that the increase in global temperature should be below 2 degrees Celsius.”
| During his visit to the COP26 climate summit in Glasgow, Scotland, Rep. Garret Graves (R-La.) explained how he talks to his party about the climate crisis. (Casey Silvestri/The Washington Post) |
Under the accord, countries would set their own emission reduction targets and plans to reach those targets, but agreed to the long-term temperature goal to limit “the increase in the global average temperature to well below 2C above preindustrial levels.”
Countries would also pursue “efforts to limit the temperature increase to 1.5C above preindustrial levels, recognizing that this would significantly reduce the risks and impacts of climate change,” according to the text.
The two targets, one firm and one aspirational, represented a fierce policy debate.
Developing countries had been pushing to set a rise of 1.5C as a target for years. Small island nations were often the most vocal in their support, pointing to the existential threat they faced.
Around the world, many adopted the slogan “1.5 to stay alive.”
Has there been a movement toward a 1.5C target?
The Paris agreement represented a significant shift. More than 100 countries expressed support for a target of 1.5C, including for the first time some major emitters.
Notably, the United States got on board, joining a group called the “High Ambition Coalition” founded by the Marshall Islands in 2014.
Scientific pressure played a role in the change. In a paper published during COP21, Nature Geoscience stated that “no scientific assessment has clearly justified or defended the 2° C target as a safe level of warming, and indeed, this is not a problem that science alone can address.”
But there remained some skepticism, with oil and gas producing Saudi Arabia among the countries pushing back on the more ambitious targets. Some officials argued that countries should keep to the less ambitious target so that countries were not set up for failure.
Former president Donald Trump pulled the United States out of the Paris agreement and promoted the use of fossil fuels.
But, under President Biden the United States has not only rejoined that agreement but also the group of nations that say that 1.5C should be the standard.
However, the U.S. leader has also privately questioned whether even the 2C goal is attainable if top emitters do not stick to their pledges. And while the draft released from COP26 on Wednesday did include new terms, it did not set 1.5C as a target.
What does the science say about the difference between 1.5C and 2C warming?
The Intergovernmental Panel on Climate Change (IPCC), a U.N. body responsible for assessing the scientific research on climate change, has warned that even an increase of 1.5C of global warming would result in significant differences, with increased heat waves and short cold seasons.
At 2C, however, the changes will be more profound. “With every additional increment of global warming, changes in extremes continue to become larger,” the IPCC wrote in a report released earlier this year that evaluated more than 14,000 papers.
The IPCC has found that an extreme heat event that would have occurred once per decade in a climate without human influence, would happen 4.1 times a decade at 1.5C of warming. It would occur 5.6 times at 2C. Other events such as heavy precipitation or drought would also increase.
The IPCC also noted that it was very likely that the relative sea level will continue to rise throughout the 21st century and beyond, and the level it rises will be affected significantly by the level of climate change.
If temperatures are confined to an increase of 1.5C, over the next 2000 years sea levels could rise by as much as 10 feet, but it could be double that if temperatures grow by 2C, the IPCC research found, and potentially worse if ice sheets in Antarctica become destabilized.
Individual papers have spelled out similar scenarios, though they also show that increases of over 2C could be far worse. The Met Office study released on Tuesday found that while a 2C increase would result in the number of people living in areas affected by extreme heat stress rising from 68 million today to 1 billion, a 4C rise could see nearly half of the world’s population living in those areas.
What are we at now?
A Washington Post analysis of multiple data sets has found that Earth has already warmed more than 1 degree Celsius on average over the past century. Some places may already have seen rises of 2C.
In their latest report, the IPCC estimated that under the current scenario, the world would likely hit the 1.5C threshold by 2040. Under the most optimistic scenario presented in the report, global temperatures would reach 1.5C by the middle of the century and then drop back down as emissions were cut further, potentially avoiding some of the worst outcomes.
Under the worst scenario envisaged by the IPCC, the best estimate was that the world will likely see a rise of 4.4C by the end of the century — with an extreme impact on life on Earth.
Links
- U.S., China issue joint pledge to slow climate change in the next decade
- Cities are the focus of COP26 on Thursday. Here’s what you need to know.
- Why has it been so hard to get fossil fuels mentioned in U.N. climate deals?
- As details of COP26 deal emerge, a push to cut emissions faster and phase out fossil fuels
- Complete coverage from the COP26 U.N. climate summit
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