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Did global warming cause this year’s storms?

By Mike Slattery
Director, Institute for Environmental Studies

The questions I have been asked most frequently over the past few weeks are these: “How much of the increase in tropical storm activity is due to global warming? And to what extent, if any, are we accelerating the process?”

These are loaded questions to be sure. I would argue that no environmental issue has sparked such fierce debate, and polarized so many, as the so-called greenhouse effect and global climate change.

In the last decade, there have been many news reports of bigger floods, more numerous hurricanes and hotter summers. This seems hard to ignore and provides fuel for the environmental lobby.

But the weather fluctuates tremendously, both in time and in space. It is driven by such things as temperature changes in the tropical Pacific and hazes from volcanic eruptions. Individual storms, floods and heat waves – even record-breakers, even decade-long strings of them – do not a trend make.

It takes many decades to make trends clear. And special interests groups, specifically those who question the validity of global warming, often use this argument as justification for adopting a more “wait-and-see” approach.

This point is worth stressing, for it is one key to understanding why there has been so much controversy over global climate change.

The thermal effect of CO2 and other greenhouse gases has never really been controversial, and long-term CO2 records have shown a significant increase in levels over the past 50 years. Furthermore, the surface temperature record, itself not devoid of controversy, has also shown an increase of about 1 degree Celsius over the last century (with a projected increase of a further 1–3 degrees Celsius over the next 100 years).

It seems logical, then, to suggest that in a warmer world, ocean temperatures will rise and this will lead to an increase in the frequency and magnitude of storms such as hurricanes.
Ocean temperatures are ultimately the key, for it is the enormous amount of latent heat that is released into the atmosphere, through evaporation and subsequent condensation of warm water that fuels these storms. But the fact is we simply cannot at this stage link this string of intense storms to global warming. Long-term data from the National Hurricane Center in Miami show that we are in a period of heightened hurricane activity that began in 1995 and could last another decade or two.

Many scientists agree that the increased activity is due to natural fluctuations and cycles of hurricane activity driven by the Atlantic Ocean itself, along with the atmosphere above it, and not enhanced substantially by global warming. Indeed, many scientists suggest that the string of major storms that have struck the southeastern United States over the past two seasons signal a return to normal.

The fact that many believe that global warming will not be a factor in hurricane activity for at least another 100 years should not be used as a rationale for complacency in the climate change debate.

Today the controversy centers on whether the greenhouse effect is already affecting climate and weather and on whether global warming will actually have a significant impact on the Earth.

Is global warming really a threat? Most scientists would respond: Absolutely! One thing that scientists do agree upon is that the future is highly uncertain, and climate models, the backbone of climate prediction, inherit this uncertainty.

But the evidence continues to mount that the Earth is undergoing significant warming and will most likely continue to do so. But by how much?

The answer, my friend, is blowin’ in the wind.

Comment at tcumagazine@tcu.edu.