Forrest Wilder at the Texas Observer reports on Texas State Climatologist John Nielsen-Gammon’s testimony to the legislature. Among the points made:
- The current drought ranks as the third worst on record, behind the ’50s and 1915-1918. But if Texas is still in drought by the end of summer it will move into second place.
- The official long-range forecast says odds are slightly tilted toward dry conditions through remainder of winter and spring. It’s also warmer than normal.
- We are also in a multi-decade period of increased drought susceptibility based on temperature patterns in the Atlantic and Pacific oceans. Once one or both patterns change, Texas should return to relatively wet conditions.
“At present the climate records in the state indicate an overall increase of total rainfall which may or may not be climate change related. The triggering factor of El Niño and La Niña, we don’t know how that will change because of climate change. The only factor related to the drought that can be clearly related to climate change is the change in temperature. The state temperature has increased on average about 2 degrees Fahrenheit since the 1970s. … That aspect of the drought is being made worse by climate change.”
Emphasis added. I have disagreed with John on matters of emphasis in the past, but this in particular is elegantly and precisely worded.
There is a difference between causality and attribution which is not well-understood by the public. Something may cause something else without the cause being provable. It is possible that most of the recent conditions are part of anthropogenic climate change. Indeed, as Kevin Trenberth points out, nothing happens to the climate that is not part of a changed climate. But that doesn’t mean that the statistical evidence is there for such attribution yet. It’s possible that such attribution may emerge over time. (As a Texan I hope it doesn’t! It’s hot and dry enough as it stands.)
In fact, we have no consensus on what happens to the El Niño behavior under anthropogenic climate change, and Texas is one of the places where this looks (at least based on past heuristics) to be important.
But the reduction in rainfall, as well as the increase in temperature, are coherent with predicted trends. Texas climate is notoriously noisy and it will be a long time before this is a slam dunk. What we are seeing looks as if it is forced. Perhaps it is fair to say that more likely than not it is part of a long term trend toward desertification. But it is also fair and succinct to say that other than the observed heating trend, the drought is not “clearly related” to human forcing.