The UN Climate Action Summit: What does “two degrees” of warming really mean for North Carolina?

The UN Climate Action Summit: What does “two degrees” of warming really mean for North Carolina?

Image: Adobe Stock

On September 23rd, leaders from around the world met in New York for the UN Climate Action Summit. Four years ago, in Paris, it was agreed to limit global warming to less than two degrees Celsius to stave off dire consequences for our planet, but too little has changed since then. Now world leaders meet again to determine a new set of actions to avoid this daunting threshold.

“Two degrees” of warming is a global number, and it doesn’t sound very big. That’s less than four degrees Fahrenheit, and here in North Carolina, the temperature rises four or five times more than that between dawn and a sunny afternoon.

But that small number is deceptive. We typically measure global warming by a change in the average climate, but when the average climate changes, extremes change more. The greatest impacts of climate change come from these previously unheard of extremes, with dangerous implications for North Carolina.

There are three main areas where this change will play out: heat, rain, and salt. To some extent, these are already happening, and all three have their greatest impacts on our farms and rural areas.

Heat: Extreme high temperatures stress plants, and during droughts they quickly dry out the soil, so much so that the new term “flash drought” has been coined. But it is people and livestock who are most vulnerable to heat. Farm work, along with construction and some athletic training must be done outside. More than just the actual temperature, people (and animals) are affected by the heat index, or the “feels like” temperature, which combines the effects of heat and humidity. When the heat index is above 105 anyone, no matter how young and healthy, is at risk of heat-related illness or even death.

If no action is taken to limit global warming, the number of days each year on North Carolina’s coastal plain with a heat index above 105 is expected to increase from a few days now to more than 25 days by the middle of this century. On those days farmers will either have to stop working or face potentially deadly risks. At the same time, this extreme heat will stress livestock and increase what farmers have to pay for energy and equipment to keep their animals cool.

Rain: Because a warmer atmosphere “holds” more water vapor, heavy rains increase when climate warms. “Two degrees” of warming would bring about a 14% increase in the heaviest rains. We can already see this happening now. Since the 1960s, the number of days each year across the Southeast with more than three inches of rain has increased nearly 10%.

In North Carolina hurricanes produce the most extreme rains. And hurricanes make more rain in a warmer climate, especially if the ocean warms. Just look at last year’s Hurricane Florence, which produced the second largest amount of water on record from a single storm in the US. Unusually warm waters in the North Atlantic boosted Florence’s rainfall totals, and Florence caused over a billion dollars in loses to North Carolina agriculture, almost all from its flooding rains.

Salt: Global warming also causes sea level to rise, since the oceans expands as it warms and melting glaciers and ice sheets add water. As seas rise, our estuaries become saltier. During storms, this salty water sloshes from drainage ditches into fields on the eastern coastal plain, making soils salty enough to threaten the productivity of farms and forests.

These outcomes – unprecedented heat, flooding rains, and unproductive soils – will impact everyone, but farmers and rural areas will be hit especially hard.

Prof. Walter Robinson – Image: NC State

So what can we do? Because some continued warming and sea-level rise is “baked into” the climate system, we cannot completely stop these things from happening. But by reducing our greenhouse gas emissions, we can choose a two-degree warmer world instead of one warmed by three or four or five degrees. This would go a long way toward avoiding the most damaging extreme outcomes of climate change. That is the message of the UN Climate Action Summit, and, given the implications of climate change for North Carolina, everyone in our state has reason to hope they succeed.

Walt Robinson, PhD, is Professor of Atmospheric Sciences at NC State University. He is a fellow of the American Meteorological Society and a member of the Scholars Strategy Network.