Asbury Park Press

The intensity of Hurricane Dorian, which recently cut a destructive swath through the Bahamas, has been seen by some as a consequence of climate change. In the aftermath of Dorian, Rep. Alexandria Ocasio-Cortez said, “This is what climate change looks like.” Democratic presidential candidate Bernie Sanders said "Hurricane Dorian has everything to do with climate change, which is the existential threat of our time.” Is there a link between recent devastating hurricanes and climate change? We posed this question and related ones to David Robinson, state climatologist at Rutgers University.

Has climate change produced more deadly, destructive hurricanes?

The general understanding is that tropical systems are infrequent enough that it is premature to state with high confidence that tropical systems have become stronger in the current warming world. As climatologists we must be patient before concluding any sort of change. Thus, we look to numerical models to explore potential change, whether it may be occurring or will be observed in the years ahead.

The general consensus at the moment is that storms should increase in intensity but perhaps not numbers as the oceans and atmosphere continue to warm. There is also recent research suggesting that storms may intensify more quickly. Best we can do with storms occurring these days (an upswing in strong storms) is suggest that their behavior may be indicative of more of them in the future.

I also like to say that, ultimately, we may look back at the present and be able to statistically confirm that change began to become apparent at this point. Of course, time will tell if that last statement will be able to be applied. Please keep some of the general statements on timing and judgment in mind as you read through the remaining answers.

Have the number of Category 4 and 5 hurricanes and extreme weather events changed over the last century?

Again, this is a matter of there being too few observations and inconsistencies in rating storms to come to a conclusion. Multi-decadal fluctuations (I don’t like to say cycles, though some studying the issue do) have been observed in Atlantic tropical system frequencies over the past century or so. Less is known on this account in the eastern and western Pacific and Indian ocean tropical regions. Thus, it is best not to say either that extreme storms have remained unchanged in number or that they have changed in intensity. We simply don’t have enough information to say either.

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Have we experienced more severe flooding and increases in storm surge in recent years? If so, is it largely attributable to global warming?

Are you talking about flash flooding, riverine flooding or coastal flooding, the latter mainly due to surge? These are infrequent enough that definitive statements cannot be made. And especially when discussing inland (freshwater) flooding, there are factors involving landscape development that must be taken into account.

Looking to the physics of the situation, one should expect more rainfall with a warmer ocean (for greater evaporation) and atmosphere (for every 1.8 degrees Fahrenheit of warming the atmosphere has the potential to hold 7% more water vapor). Fact is, both the atmosphere and oceans are warming in and near New Jersey and, of course, globally.

You still need “triggers” to generate storms (for rainfall and surge), but all other things atmospherically being equal (and we’re unsure whether they remain equal or will change in the future) and not taking changes in landscape development or flood control measures into account, we should see more fresh water flooding in the future.

Surges may or may not increase in magnitude, but they will occur “atop” higher sea level, thus even if they don’t increase in magnitude they will result in more coastal flooding. Returning to freshwater flooding, we have seen a number of major floods in New Jersey over the past 20 years on all river systems. I have seen enough to feel confident enough to state that such flooding is being enhanced by regional climate change. No one at this point can be confident enough to express this in percent increases; just call this my informed judgement.

What factors have produced sea-level rise?

There is a 2016 report out of Rutgers, in which I participated, that addresses the issue (past, present and future). However, the science is evolving so quickly that just last week our group met to begin an update of the earlier report. To boil sea level rise in New Jersey (about 15 inches over the past century) down to the basics, causes include land subsidence (post glacial isostatic effect and removal of ground water via pumping), warmer seas (thermal expansion), and the melting of alpine glaciers and ice sheets. The majority of the past century’s rise is attributed to the latter two. Those two, especially melt, are likely to play proportionately greater roles over the remainder of the century (and beyond). Isostatic adjustment will essentially remain unchanged and it is unknown if pumping of groundwater will change.

Does colder winter weather in recent years suggest that the planet is not heating up?

Winters are not getting colder locally or globally. You cannot take a short-term weather event and conflate it with longer-term climate change. There is overwhelming evidence that the global atmosphere and oceans are warming at a rapid pace. Certainly, variations in weather will continue to occur within this warming world. And there is enough seasonal and interannual short term climate variability that there will not be monotonic warming — i.e. each winter, each year being warmer than the last….

Is it too late to reverse the damage from global warming?

This is far too complex of a science and social science discussion to hardly begin answering here. I would just suggest that it is logical to consider both mitigative and adaptive approaches to the issue. My opinion (yes an opinion) is that should we choose to ignore one or the other, society does so at its own peril.

How, exactly, do increases in carbon adversely affect the atmosphere? How does that translate into warmer temperatures in our oceans and land areas?

Greenhouse gases, such as carbon dioxide and water vapor, delay the exit of energy from the earth-atmosphere system that arrives from the sun. This delay warms the atmosphere, thus the more gases, the more atmospheric warming.

One general analogy to explain this is a blanket on a bed. The human under the blanket is producing the heat, but the idea of the blanket slowing the loss of heat away from the body is somewhat the same as an atmospheric “greenhouse blanket.” The heat will eventually escape into the bedroom (otherwise the sleeper might burst into flame!). The warmth released into the bedroom roughly balances that being generated by the sleeper. However, the sleeper is warmer than if no blanket was over them. Now if the person is still too cool under the blanket, they can add another one. Yes, a further delay in heat leaving the “atmosphere” near the sleeper.

Now think of adding greenhouse gases to the atmosphere. This will result in a warming of the atmosphere until a new thermal equilibrium is reached under/within the blanket, unless, of course, the gases continue to increase, in which case warming will continue. Simple physics.

David A. Robinson is New Jersey state climatologist at Rutgers University.