Explained: 1.5 C Climate Benchmark | MIT News

in 2023 summer was a season of extreme weather.

June wildfires raged in parts of Canada, smoke billowed into the US and air quality issues were reported in dozens of downwind states. In July, the world recorded the highest temperature in the world, which lasted for three days in a row, before breaking again on the fourth day.

From July to August, unrelenting heat gripped much of Europe, Asia and the United States, while India faced a monsoon season, with heavy downpours inundating the northeastern regions of the United States. a historic fire ravaged Maui, destroying the entire town.

These extreme weather events are largely the result of climate change caused by humans’ continued burning of coal, oil and natural gas. Climate scientists agree that extreme weather like the one humans experienced this summer is likely to become more frequent and intense in the coming years unless sustained and planet-wide action is taken to curb global temperatures.

Just how much control are they talking about? The internationally agreed figure is 1.5 degrees Celsius. To avoid worsening and possibly irreversible effects of climate change, global average temperatures should not exceed pre-industrial temperatures by more than 1.5 degrees Celsius (2.7 degrees Fahrenheit).

As more and more regions of the world face extreme weather conditions, it is worth considering the 1.5 degree band where the planet is in relation to this threshold and what can be done at the global, regional and personal levels to ‘keep 1.5 alive’.

Why 1.5 C?

In 2015, in response to increasing climate impacts, nearly all of the world’s countries signed the Paris Agreement, a landmark international treaty in which 195 countries committed to keeping the Earth’s temperature “well below 2 degrees Celsius compared to pre-industrial levels. levels’ and continues to aim to ‘limit the temperature rise to 1.5 degrees Celsius above pre-industrial levels’.

The treaty did not define a specific pre-industrial period, although scholars generally consider 1850-1900 to be a reliable starting point. this time predates the use of fossil fuels by humans, and is the earliest period for which global land and sea temperatures can be observed. During this period, the average global temperature, while fluctuating up and down in certain years, was generally around 13.5 degrees Celsius, or 56.3 degrees Fahrenheit.

The agreement was informed by a fact-finding report which concluded that global warming of even 1.5 degrees Celsius above the pre-industrial average would pose significant risks to “some regions and vulnerable ecosystems” over long periods of decades. A limit of 1.5 degrees Celsius was then recommended as a “line of defense” – if the world could stay below that limit, it could potentially avoid the more extreme and irreversible climate effects of a 2 degree Celsius rise. in some places even a smaller increase.

However, as many regions are experiencing today, keeping below the 1.5 line does not guarantee that the extreme effects of global warming will be avoided.

“There is nothing magical about the number 1.5, except that it is an agreed aspiration. Maintaining a 1.4 is better than a 1.5, and a 1.3 is better than a 1.4, and so on,” says Sergey Paltsev, associate director of MIT’s Joint Program on Global Change Science and Policy. “The science does not tell us that if, for example, the temperature rises by 1.51 degrees Celsius, it will definitely be the end of the world. Similarly, if the temperature remains at 1.49 degrees, this does not mean that we will eliminate all the effects of climate change. What is known: The lower the temperature target, the lower the risk of climate impacts.

How far are we to 1.5 C?

In 2022, the average global temperature was about 1.15 degrees Celsius above pre-industrial levels. According to the World Meteorological Organization (WMO), the cyclical weather phenomenon La Niña recently contributed to a temporary cooling and softening of the effects of human-induced climate change. La Niña lasted for three years and ended around 2023. March.

In May, the WMO published a report predicting a high probability (66 percent) that the world will exceed the 1.5 degree Celsius threshold in the next four years. This breach is likely due to human-induced climate change combined with a warming El Niño, a cyclical weather phenomenon that temporarily warms ocean regions and raises global temperatures.

An El Niño is currently underway this summer, and the event typically increases global temperatures the year after it begins, which in this case would be 2024. The WMO predicts that for each of the next four years, global average temperatures are likely to vary between 1.1 and 1.8 degrees Celsius compared to pre-industrial levels.

Although there is a good chance that El Niño will make the world warmer than the 1.5 degree threshold, the breach would be temporary and would not yet break the Paris Agreement, which aims to keep global temperatures below the 1.5 degree threshold in the long term (on average within a few decades rather than a single year).

“However, we should not forget that this is a global average and there are regional and seasonal differences,” says Elfatih Eltahir, HM King Bhumibol Professor and professor of civil and environmental engineering at MIT. “There have been extreme conditions around the world this year, even though we have not reached the 1.5C threshold. So even if we manage the global average, we will see extreme events due to climate change.

More than a number

According to the Intergovernmental Panel on Climate Change (IPCC), in order to keep the long-term average temperature of the planet below the threshold of 1.5 degrees, until 2050 the world will have to achieve zero emissions. This means that in terms of emissions from burning coal, oil and natural gas, the entire world will have to remove as much as it puts into the atmosphere.

“When it comes to innovations, we need them all – even those that may seem quite exotic at the moment: fusion, direct air capture and others,” says Paltsev.

The task of curbing emissions in a timely manner is particularly daunting for the United States, which emits more carbon dioxide than any other country in the world.

“U.S. fossil fuel burning and energy consumption far outpace the rest of the world. It’s an ongoing problem,” says Eltahir. “And national statistics are the totality of many people’s activities.”

On a personal level, there are things that can be done to reduce personal emissions and potentially offset rising global temperatures.

“We are consumers of products that contain greenhouse gases, such as meat, clothing, computers and homes, or we are directly responsible for emitting greenhouse gases, such as when we use cars, airplanes, electricity and air conditioners,” said Paltsev. says “Our daily choices affect the amount of pollutants we emit into the atmosphere.

But getting people to change their emissions may be less about numbers and more about feelings.

“In order to get people to act, my hypothesis is that you need to reach them not only by convincing them to be good citizens and saying that keeping the world below 1.5 degrees is good, but also by showing them how it will affect them individually,” says Eltahir. , who specializes in regional climate research, focusing on the effects of climate change on the water cycle and the frequency of extreme weather events such as heat waves.

“Real climate progress requires dramatic changes in how the human system obtains energy,” says Paltsev. “It’s a huge commitment. Are you ready to make personal sacrifices and change your lifestyle? An honest answer to this question would help explain why real climate progress is so difficult to achieve.

Godfrey Kemp

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