Extreme Temperature Diary-March 21, 2018/ Topic: Hindcasts and Forecasts

Wednesday March 21st… Dear Diary. The main purpose of this ongoing post will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials)😊. Here is today’s main climate change related topic: 

Hindcasts and Forecasts

Welcome to spring 2018. Segueing from yesterdays topic on the five stages of climate change denial, any person studying, writing or blogging about global warming with any credibility needs to point to what are termed “hindcasts,” which verify climate model projections. Now that it is the year 2018 there have been nearly thirty years since 1990 to see how well climate models have been doing since the first IPCC assessment. Hindcasts are doubly important to look at because models that do better with them are more than likely superior forecasting global warming conditions in the future. On these posts I usually highlight the work of one climate scientist at a time. Today it is Zeke Hausfather’s turn:

For a good animation on hindcasts since the 1970s see: https://www.instagram.com/p/BZ38rf7F3al/
Zeke’s chart is interesting in that the thing indicates that global warming forecasts since 1990 were a tad above what verified. Historically climate change denialists have harped on this slight deviation to sustain their arguments that any warming won’t be that significant. I contend along with Dr. Jerry Meehl that the first IPCC from 1990 was a little two aggressive with warming trend forecasts trough the year 2020 not taking into account enough heat absorbed by the Earth’s oceans. In any case it appears that any “delay” in warmth is no more than about 5-10 years, which in the broad scheme of things as far as the fate f humanity goes s a very moot point. Here is more from Zeke:

Longer we wait to reduce emissions, steeper the reductions need to be to avoid >2C warming. Next few years critical.

In the debate over “how soon and how much”  briefly see here from Zeke that hindcasts are a crucial key to the proverbial puzzle we are all trying to piece together. If anyone wants to get a good primer on climate models see:

Speaking of the consequences of climate change in association with the “how soon and how much” debate Bob Henson has come up with a superb summary of work going on to determine if climate change is strengthening winter storms: https://weather.com/science/environment/news/2018-03-21-climate-change-winter-weather

In light of the fact that “Toby” is pounding the Northeast today, here are some quotes from Bob: 
“In their latest study, Cohen and colleagues examine U.S. winter weather at 12 U.S. cities from 1950 to 2016 via the Accumulated Winter Season Severity Index, or AWSSI. The index uses temperature, snowfall, and snow-depth thresholds to calculate how rough a winter has been at each location. The researchers compared AWSSI values to temperature and air pressure in the Arctic, north of latitude 65°N and up through the stratosphere to about 100,000 feet.”
“A strong relationship between a warmer Arctic and increased frequency of severe winter weather is apparent for all stations east of the Rockies, with the strongest association in the eastern third of the US,” the scientists reported. The links were stronger for cold temperatures than for snowfall, although the team found a robust correlation between Arctic warming and increased heavy snow in eastern cities.”
“The increasingly strong correlations between AWSSI and a warm Arctic do not prove cause and effect, as the authors acknowledged. It’s possible that some third factor, such as changes in tropical oceans, could be driving both Arctic warming and midlatitude winter weather. To get at this question, the authors examined whether Arctic warming preceded or followed U.S. winter weather events. They found that AWSSI values tended to be highest about five days after the Arctic warming, which suggests that the Arctic plays at least some role in triggering the U.S. cold snaps and snowstorms.” 
“Several experts in climate change and midlatitude weather are not yet convinced that changes in the Arctic are leading to an increase in extreme U.S. winter weather. “The basic findings are sound, but I would take issue with some of the interpretation in the study,” Michael Mann (Pennsylvania State University) told the Los Angeles Times.”
So, what we are seeing this month fits the “more and stronger” hypothesis in association  with winter storms and climate change: 
I’ll be posting more in Toby as the day progresses.
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The Climate Guy

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