Extreme Temperature Diary- Sunday December 3rd, 2023/Main Topic: What’s the big deal about Earth getting 2°C hotter?

What’s the big deal about Earth getting 2°C hotter? (nationalgeographic.com)

Just 2°C may not sound like a large increase, ​but scientists say it has potential to cause ​extreme ​weather ​around the world and destabilize ​the climate. 

What’s the big deal about Earth getting 2°C hotter?

The increase may sound inconsequential, but scientists say there are serious ramifications for life as we know it if the planet exceeds the climate target.

Thirty-five years after NASA scientist James Hansen testified before the United States Congress about the specter of climate change, Earth is on pace to experience 2.7°Celsius (4.9 degrees Fahrenheit) of warming by 2100. And while there is little consensus among nations about how and how fast to reduce the carbon emissions that are responsible for that warming, there is near universal consensus that this temperature increase would be disastrous.

For that reason, the 196 signatories to the Paris Agreement, signed in 2015, committed to keeping the mean rise in global temperatures below 2° C (3.6° F) above pre-industrial levels and preferably limit any increase to 1.5° C (2.7° F). Participants in the 28th United Nations Climate Change Conference (COP 28), taking place in Dubai November 30-December 12, will be expected to update their progress on meeting those goals.

Given that the globe is already about 1.2 °C (2.2° F) warmer than it was before the Industrial Revolution, that target may seem, depending on your level of optimism, either highly ambitious or perfectly within reach. But what exactly does this goal save us from, and how was it selected in the first place? 

How 2° C became a target

According to Daniel Swain, a climate scientist at the University of California Los Angeles (UCLA), the targets are as much political as scientific.

“Ultimately, there is nothing geophysically sacrosanct about 1.5, or two, or three, or any other particular number,” he says. What’s more important to recognize, he argues, is that with every incremental degree of warning, the greater the likelihood that Earth will reach irreversible “tipping points”— or, as he puts it, “the more likely it is that we experience what I sometimes call unpleasant surprises.”

Furthermore, explains Maria Ivanova, director of the School of Public Policy and Urban Affairs at Northeastern University, the concept of limiting warming to two degrees significantly predated the Paris Agreement. It was, she says, a “back of the envelope calculation” in the 1970s by an economist at Yale, William Nordhaus, who argued in a pair of papers that a two-degree increase would push the climate beyond the limits of human experience.

(Which cities will still be livable in a world altered by climate change?)

However, it would be wrong to infer that two degrees was just plucked from thin air, cautions Michael Mann, director of the Penn Center for Science, Sustainability and the Media at the University of Pennsylvania.

“Clearly there is no absolute threshold,” he says. “It’s more a somewhat objective definition of where we move from ‘bad’ into ‘really bad’ territory. Two degrees Celsius is a reasonable dividing line where we cross into the ‘red’ across all areas of concern.”

Some places are warming more quickly than others 

Is two degrees in fact too much warming?

“Well, 1.2°C warming, which is where we are, is too much,” says Mann. “We’re already seeing devastating consequences. So, it’s really a question of just how bad we’re willing to let it get. 1.5°C would be bad, two degrees really bad, and three degrees is perhaps, as I argue in my new book Our Fragile Moment, civilization ending.”

Mann notes that a 2018 Intergovernmental Panel on Climate Change (IPCC) report found that the difference between 1.5°C of warming and two degrees could be devastating.

“Basically, what it shows is that the additional 0.5°C of warming would likely mean the loss of Arctic sea ice, three times as much extreme heat, far greater levels of extinction and the possible loss of coral reefs across the planet. It would take us even closer to the tipping points for loss of Greenland and West Antarctic Ice Sheets (and the meters of sea level rise that go with it). Pretty stark stuff,” he says.

(Could billions of oysters protect coastlines from rising seas?)

Additionally, of course, an average global increase is just that— an average. Some places, such as the Arctic, are warming four times more quickly than the rest of the planet; what may seem like a moderate amount of sea level rise in parts of the United States, could be catastrophic in low-lying Pacific Island states. 

For that reason, such states have been at the forefront of emphasizing the importance of limiting warming to 1.5°C.

A case for temperature targets 

But if 1.2°C degrees of warming is already too much, and two degrees is potentially cataclysmic, should we be setting our targets lower? Should we even be worrying about temperature targets at all?

“It is imperative to have a target,” argues Ivanova. “Having a goal is critical. It is like having a speed limit, particularly when you think about how speed limits are communicated. It is one thing when you have a static sign that says 60 miles an hour. But it is another thing when you are nearing one of those signs that flashes your speed at you. Because then what you do is you push the brakes because that real time feedback of ‘Oh, I am above the limit,’ actually does lead to behavior change.”

However, argues Swain, the brakes are not even close to being pumped enough right now.

“If we could wave a magic wand and [eliminate] carbon emissions tomorrow, we probably could keep [the increase] under 1.5°C degrees,” says Swain “But of course, we can’t; that magic wand does not exist. And I think the same thing is largely true of two. I think two degrees is also at this point, a very ambitious target relative to our current trajectory.”

It is unquestionable, Swain acknowledges, that there has been a lot of progress toward reducing carbon emissions.

“Are we on a much better path than we were in, say, 2005? Yes, we are. There has been an explosion in clean energy. There’s incredible science going on. There have been tremendous public policy successes.” But, he argues, much more is needed, at a far quicker rate, for warming to not only slow down but stop.

If that can happen in time to prevent Earth warming by two degrees, then that would be an achievement of sorts. But if it can be done well before that threshold is reached, that would be a significantly greater success for all.

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