The Earth’s average global temperature is 1.2 degrees Celsius (around 2.2 degrees Fahrenheit) hotter than in preindustrial times, causing shifts in weather patterns and more frequent and severe extreme weather events such as storms and droughts.
This global warming, also known as climate change, is the result of humans filling the air with gases that intensify a process called the greenhouse effect.
The greenhouse effect occurs when the sun’s rays reach the Earth’s atmosphere and the majority of the radiation bounces back out into space. When this happens, a small portion is absorbed by chemicals in our atmosphere. These are known as greenhouse gases.
By looking at air bubbles from hundreds of thousands of years ago until today, scientists have found that temperatures go up or down in lockstep with the amount of greenhouse gases like methane and carbon dioxide.
Human activity has started to change the delicate balance of chemicals in our atmosphere.
Since the dawn of the industrial revolution, humans have been burning fossil fuels such as coal, oil and natural gas for energy. When these substances are burned, they emit excess greenhouse gases, mostly in the form of carbon dioxide.
According to measurements taken in February and March from the Mauna Loa Observatory in Hawaii, carbon dioxide in the atmosphere is now reaching levels 50 percent higher than in the preindustrial period. More greenhouse gases means more heat trapped in the atmosphere and, over time, a warmer planet.
When the average temperature of the Earth is raised, even by just a few degrees, we see some pretty dramatic effects. For example, it can cause a rise in ocean temperatures that can lead to more extreme storms and flooding.
Klaus Jacob, a special research scientist at the Lamont-Doherty Earth Observatory in New York, explained one consequence of warmer oceans.
“As the ocean gets warmer, it expands,” Jacob said. “So as sea level rises, you need only smaller and smaller storms to reach the same elevation in New Orleans, or New York City, or anywhere else where we have storms. ... And so you get much more frequent flooding.”
At the same time, some areas are dealing with long droughts because warmer temperatures cause more evaporation and dry out the land and vegetation, which leads to problems like crop shortages and widespread forest fires.
The severe current, and potential future, consequences of climate change were laid out in a landmark report conducted by the U.N.’s Intergovernmental Panel on Climate Change, which was released in August.
The assessment found that if the world follows the scenario of very low greenhouse gas emissions, it’s plausible that warming of greater than 1.5 or 2 degrees Celsius above preindustrial temperatures can be avoided.
But if that scenario — which involves very drastic, rapid and sustained cuts in carbon dioxide and other greenhouse gases, enforced by governments and businesses — is not followed, the world could be heading toward being 3 degrees Celsius warmer by 2100.
In all cases, there will be more extreme events like hurricanes and heat waves that cause flooding, wildfires and droughts. It’s only a question of how severe we allow the situation to become.
When it was published, the report was described as “a code red for humanity” by U.N. Secretary-General António Guterres.
The U.N. timed the report’s release to lead into the U.N. Climate Change Conference, also known as COP26, in Glasgow, Scotland. The ongoing fight to limit global warming and to deal with its effects hinges on successful talks between world leaders at the conference, which will take place in early November.
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