Texas is not immune to the effects of increasing greenhouse gases, according to the state climatologist, John Nielsen-Gammon, of Texas A&M University’s Department of Atmospheric Sciences. Dr. Nielsen-Gammon also says the international science on climate change is fundamentally sound despite challenges from state officials, and the drought in Central Texas is likely to continue. Below are excerpts from an interview with the Texas Tribune.
In Texas, the overall climate pattern vaguely follows global pattern for temperature change, with warming in the early part of the century, then fairly flat in the middle and warming since then. A part of that is due to an increase in greenhouse gases. And the computer models — just atmospheric models — that are run with historical sea-surface temperatures give this same pattern, so basically you’ve got the sequence of events: the warming, the change in the radiative properties of the atmosphere affecting the ocean temperatures, which in turn affect things locally. There’s a lot of natural variability that goes on top of that, so it’s not really possible at this point to say what fraction is due to global warming, but based on what we know, it seems like a significant fraction of it is.
The model projections [about the impact of greenhouse gases on climate] that are run for the IPCC [Intergovernmental Panel on Climate Change] have the temperatures rising in Texas from the present by an additional anywhere from 1 to 4 to 5 degrees by the middle of the 21st century. And the rate of rise projected there is similar to how rapidly temperatures have been rising since the 1970s, so it’s at least plausible that that could happen. Part of the problem is there’s a big range in that forecast, so it could go up a little or go up a lot. Even a little bit would put that warmer than anything we saw in the 20th century.
But those are just considering one factor involved in climate change. You’d also have to consider the effects of aerosols and volcanic activity and solar intensity and the Pacific Decadal Oscillation — all sorts of things we can’t predict. So we don’t know what temperatures will be like in 2050. What the projections tell us is basically the effect of greenhouse gases alone would give us that much warming. And the other factors could have just as big an influence, but it could go in either direction. Maybe they’ll cancel the greenhouse warming and we’ll stay about the same. Or they could be a positive factor on top of it. So those are the things that we can’t predict. But we can say the increase is definitely caused by humans.
The regional variations will come from the other effects, not the greenhouse gases per se. The greenhouse gas effects will be fairly uniform. The specific pattern of temperature change depends a lot on the specifics of how the ocean temperatures evolve. Even in the past century, the rise has not been uniform across the state. East Texas is still cooler than it was in early part of 20th century, whereas South Texas is quite a bit warmer than it has been. So there’s already quite a bit of variation. Likewise, that variation is not predictable either, so it may be that East Texas will catch up, and it may be that the pattern will persist. We just don’t know.
The good news about preparation is that climate change is a slow process. The impacts happen relatively suddenly, though. For example, there are two main factors in Texas affecting sea-level rise. The most important one is land surface subsidence, through freshwater pumping and other factors. Second in importance is the global sea-level rise due to climate change. But the cause doesn’t really matter for adaptation purposes. Where sea-level rise has an impact is not the gradual up-creep of the shoreline but the sudden change of shorelines associated with major hurricanes and other storms that have reconfigured the coast. Infrastructure needs to plan for the net effects of sea level rise for anything that’s supposed to last for decades. So major ports and shipping facilities, refineries and power plants have to be able to able to adjust for the likelihood that over the next several decades, the local sea level’s going to be increasing by a foot or more. And that’s likely to continue.
The other big adaptation that’s probably going to take place is in terms of agriculture. As the climate changes, the crops that are viable or most profitable change also. That sort of thing, farmers have been adjusting to for years. There are periods of times when citrus was growable in certain areas, and periods of time when it wasn’t. Farmers can be on their toes and forward-looking about this. In other words, things that are presently marginal (because of cold temperatures in the wintertime) will gradually become more and more viable with time. And conversely, plants — agricultural products — that have difficulty with heat can be expected to have more difficulty in the future.
Hurricanes: Presently, the models come up with about the same number of hurricanes or even fewer hurricanes. So the present thinking is that they’re probably not going to become more frequent in the future; however, the ones that do develop will have the potential to become more intense. Just like temperatures, though — even more so than temperatures — the details of that pattern will vary from region to region, because there are other things besides temperatures that affect where hurricanes form and how they intensify. So for any given location, at this point, it’s literally too early to tell whether the net effect of hurricanes would increase or decrease.
Drought: We went into this fall and winter with the expectation that it was going to be dry, because we had unusually cold sea-surface temperatures in the eastern tropical Pacific. It’s a phenomenon called La Niña. It’s essentially the opposite of El Niño, which has warmer temperatures there. And that affects the thunderstorm pattern over the whole of the Pacific, and that in turn affects the jet-stream pattern and so forth. The bottom line is when that happens, most of the time Texas — and, for that matter, just about all the U.S. — ends up having a relatively warm and relatively dry winter. So that part was not a surprise. It’s especially hit hard in Central Texas. Most of the Panhandle is doing fine, but otherwise, yes, the past couple of months have been dry. Looking at the numbers, it seems that in some places it may very well be that this past October and November were the driest on record, ever.
It’s unlikely it will stay this dry. I don’t expect every month to be record-setting dryness. But it’s certainly likely that we’ll have below-normal rainfall going on. I’ve looked at a few of the cases in past, where we’ve had exceptionally strong La Niña events like we do now. It seemed like for them it was dryer in the fall than it was in the spring. So that’s a little glimmer of hope, but it’s still not going to be a particularly wet winter even if that pattern holds true.
We talked about temperatures changing in Texas. Precipitation is also changing. People may have seen reports that the southwestern United States, including Texas, is getting dryer and going to become another Dust Bowl. There’s some element of truth in that, but rainfall in Texas has actually been steadily increasing over the past century. It’s about 10 to 15 percent more rainfall per year now than there was at beginning of 20th century, which is a fairly large amount. And the projections for rainfall change in the future from climate models — some have it wetter, most have it dryer. But none of the changes is as big as we’ve already seen. So the good news in that regard is we don’t really need to worry about what climate change will do to rainfall because rainfall is already changing by a lot more than that.
The impact on water supply is going to come from the change in temperature, which increases evaporation, increases water demand and increases the need for water both by plants and by cities. So the changing climate is going to reduce water supplies, but that’s a second-order effect compared to the increase in population, which is having a massive effect on demand for water. But as we know more and more about climate change, I think it becomes more and more important that we plan for the effect of a changing climate as well as plan for the effect of a changing population.