UPDATE: John very quickly responded and I have reproduced below along with my follow-up comment.
First, I’ll write about the quote, then I’ll read your weblog post and, if necessary, respond to what you said about it.
The eight seconds shown on-air was part of a long answer to a oomplex question. As you know from http://blog.chron.com/climateabyss, my preliminary analysis of attribution of the 2011 Texas drought indicates that there’s no strong evidence that annual precipitation deficits have become more frequent or more intense as a result of global warming. Also, I concluded that most of the excess temperatures associated with the drought were directly associated with the lack of precipitation. Finally, I concluded (conservatively, I would say) that about a half degree to a degree was attributable to anthropogenic greenhouse gases.
The effect of this extra heat would be felt most strongly on the margins. For example, an ordinary drought would not have caused massive tree die-off throughout central and eastern Texas, and that nonlinear effect was enhanced by the extra heat and evaporation. Likewise, it took an exceptional drought to produce the wildfires in central and eastern Texas this fall, and there would have been fewer fires, with existing fires spreading not quite so rapidly, if not for the extra heat due to global warming. There’s no way I can say whether the Bastrop fire would not have occurred, or only have been 80% as large, or 90% as large, but I can walk up to the last house that burned on the edge of the fire and say pretty confidently that if the forest hadn’t dried out quite so much, that house would still be standing.
Much of Texas is part of the “global warming hole” in the south-central/southeastern United States, where the century-long linear trend is flat or negative. I am convinced by various studies that the warming hole is a consequence of ocean-driven natural variability locally cancelling out the global temperature trend. One consequence of this is that actual temperatures in Texas on a multi-decade scale are barely as warm as they were in the middle of the 20th century. Without much local climate change, there were no environmental changes or ecosystem changes that have taken place within Texas that could be pointed to and said of, “This happened here because of global warming.” Until now. The enhancement of the drought by global warming has made the impacts somewhat more severe than they would have been without global warming, so this drought makes it possible for the first time to point to an impact in Texas and say, “Here’s something that’s a consequence of global warming.”
Now I’ll read your blog…..(pause)….
We didn’t receive any snow in Texas from the October snowstorm. My quote was presented by NBC in the context of the Texas drought, and I don’t see how any viewer would think that I was talking about the snowstorm rather than the drought. The transcript (in the story you link to) is quite clear on this. In my interview with them, the subject of the East Coast snowstorm never came up. So I disagree with your claim that NBC used the quote “to support their claim that the October snows were just more evidence of global warming.”
As you note, my analysis does not delve into the issue of the relative contribution of greenhouse gases to global warming over the past century, but plenty has been written about this by others, including the IPCC. I chose a conservative estimate for this value (that’s the “conservative” in parentheses above). With the uncertainties over response times and feedbacks, the amount of observed warming over the past century plausibly attributable to anthropogenic increases in the concentration of greenhouse gases may be as small as 0.5F and may be as large as 2.0F, in my opinion. I picked 1.0F, but whatever the actual value is, it is unquestionably positive an enhanced the severity of the drought.
I don’t have time to engage in an extended dialogue, so I’ll go ahead and answer your next question, which I think might be, “Do you agree with NBC that events like the October snowstorm will become increasingly common with global warming?” I have not looked at this particular snowstorm, but when I wrote about the heavy East Coast storms of a winter or two ago, I argued that they were not enhanced by global warming at all. So I do disagree with NBC on that point.
Thank you for the opportunity to respond!
Hi John. Thanks for the quick feedback. I will go ahead and post your reply.
I have this point of disagreement – you are (incorrectly in my view) equating global warming with the subset of warming caused by CO2 and a few other human inputs of greenhouse gases.
Moreover, global warming is not a more-or-less monotonic warming as we can see in the MSU lower tropospheric temperature data [which I have added below from the University of Alabama data through October 2011]
I was alerted to an NBC TV news article by Brian Williams and Anne Thompson (h/t toMarc Morano and Noel Sheppard) which is titled on NewsBusters as
One of the quotes in there, from my colleague John Nielsen-Gammon, does not appear to conform, regarding the October snow news report at NBC, to what he had written earlier on the drought in Texas. At the very least, he needs to clarify his views as they were used by NBC. In the NBC interview he said
Mr. JOHN NIELSEN-GAMMON (Texas State Climatologist): This is really the first time when climate change–the impact of climate change has manifested itself in a tangible way within the state of Texas.
However, on John’s weblog in the post
he was more more precise in how he frames his view. He wrote [highlight added]
Until we learn more, it is appropriate to assume that the direct impact of global warming on Texas precipitation interannual variability has been negligible, and that the future variability trend with or without global warming is unknown.
The unanimous conclusion, based on observations, dynamics, and models, is that it’s not possible to tell whether La Niña will become more or less frequent or intense in the future under global warming.
So at present, both the PDO and AMO are properly configured to produce droughts in Texas, and this fact explains the current cluster of droughts
The combination of Atlantic and Pacific sea surface temperatures led to dry conditions during the fall, winter, and spring of 2010-2011. Local feedback mechanisms played an increasingly important role during the summer of 2011.
The actual summertime temperature was 86.8 F, so 4.0 F out of the 5.4 F of excess heat (74%) was a consequence of the drought itself.
This record-setting summer was 5.4 F above average. The lack of precipitation accounts for 4.0 F, greenhouse gases global warming [edited 9/11/11] accounts for another 0.9 F, and the AMO accounts for another 0.3 F. Note that there’s uncertainty with all those numbers, and I have only made the crudest attempts at quantifying the uncertainty.
the summer temperatures would have been about one half to one degree cooler without the increases in CO2 and other greenhouse gases. [edits 9/11/11]
Texas would probably have broken the all-time record for summer temperatures this year even without global warming. [edited 9/11/11]
Precipitation: The balance of evidence does not support the assertion that the rainfall deficit since October 2010 was made larger or more likely by global warming.
Temperature: Compared to long-term averages of summer temperature, the rainfall deficit accounted for about 4 F of excess heat and global warming accounted for about 1 F of excess heat. Warmer temperatures lead to greater water demand, faster evaporation, and greater drying-out of potential fuels for fire. Thus, the impacts of the drought were enhanced by global warming, much of which has been caused by man. [edited 9/11/11]
John’s summary is correct that, IF his analysis was correct and the global annual average surface temperature anomaly can be added to the Texas average, there would have been 0.9F addition to the temperature. This is unrealistic, of course, as Texas responds to regional climate conditions not a global average. However, even if we accept that 0.9F addition, the contribution from “global warming” using John’s numbers is just ~17% of the total positive temperature anomaly that he reports.
His statement that “much of which has been caused by man referring to global warming] is unsubstantiated in this analysis.
Indeed, as he himself writes “both the PDO and AMO are properly configured to produce droughts in Texas” and “it’s not possible to tell whether La Niña will become more or less frequent or intense in the future under global warming.” Thus, his edits, added 9/11/2011, is not justified based on his earlier discussion in his post.
Returning to the NBC nightly news quote, since John’s quote was used to support their claim that the October snows were just more evidence of global warming. I am contacting him to ask if he agrees with their assertion. I will update readers when I have a reply from John.