Understanding the Strange Phenomenon of Warming Holes and Their Causes

Climate experts have been studying the potential causes of what is referred to as "warming holes." This term is used to describe the curious divide in how a few areas of the U.S. are not experiencing the warming trend that the rest of the country has seen over the last 30 years. Here is a closer look at warming holes and what could explain this discrepancy.

What is a Warming Hole?

Scientists have offered up various explanations of why some parts of the country have not been under the gun for increasingly hotter summers. A limited warming trend, or even slight cooling, has been observed in a few pockets of the country over the last three decades when compared to a broader time period between the years 1901 and 1960. These warming holes are in sharp contrast to data from the U.S. Environmental Protection Agency (EPA). These numbers indicate that the temperatures across the Lower 48 are now 1.6 degrees warmer on average than they were back in 1896.

What is the most surprising is that this gulf in temperatures is happening during the summer months, a time when the impacts of global warming are the most glaring. Where are these warming holes located? The bulk of these pockets of less severe global warming is happening in portions of the Midwest and the Southeast. However, scientists have recently noted that the cooling trend in the Southeast is beginning to reverse itself.

Explaining the Possible Causes of the Warming Holes

There are a number of theories that could explain why some areas of the U.S. have not warmed as quickly. Climatologists believe that the dedicated effort of reforestation in the Southeast has led to cooler temperatures over the last 30 years. While the Southeast is still a major agricultural region, the abandonment of some of the farming land has led to reforestation in this corner of the country. Forested land brings up more water from the soil, sending it into the air to produce cooling cloud cover and rain showers.

In a similar vein, the effects of "corn sweat" in the Midwest could also help to explain cooler pockets of air in this region. Corn sweat is the term used to describe how corn crops naturally put more water into the air. This moisture is then transformed into cooling rain. Thus, it would make sense that the Midwest corn belt sees disproportionately cooler temperatures during the peak summer corn growing season.

Although there are several theories explaining the presence of these warming holes, the common thread is that the unexplained cooler temperatures are typically tied to rainfall amounts. This makes sense when you understand that climate change has also increased the frequency and intensity of flooding rainfall events. So while climate change may be bringing temperatures up overall, it is also producing more times of heavy rain that can have a reverse effect on the mercury during the summer season.

It is also important to note that warming holes that are noticeable during the summer months are not necessarily present over the whole year. This means that because summer makes up just a quarter of the calendar year, the overall annual temperatures may not skew warmer. However, a drop in readings compared to the historical trend during the summer will mitigate the overall change in the mercury when compared to prior years.

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