Guest Post by Bob Tisdale
Apparently, based initially on a 1975 “first intuition” by an economist (not a climate scientist), politicians have sought to limit global surface warming to 2 deg C above pre-industrial levels by restricting greenhouse gas emissions. To that end, those politicians created the political entity called the Intergovernmental Panel on Climate Change (IPCC), whose sole purpose is to prepare reports to support the politicians’ agendas.
Politicians from around the globe are once again gathering this year to futilely try to reach agreement on how to achieve that goal of limiting global warming to the economist-suggested limit. So, in order to increase public awareness, we’re being bombarded weekly with speculations of pending global-warming gloom and doom. One was a recent article Earth now halfway to UN global warming limit at NewScientist. It included a graph titled “Halfway to hell”, my Figure 1, prepared by chemist Kevin Cowtan. The graph showed that the values of most surface temperature reconstructions would likely rise above a 1.0 deg C anomaly in 2015.
AN EFFORT TO HELP NEWCOMERS UNDERSTAND
What’s novel about that graph? The anomalies (deviations from “normal”) are referenced to pre-industrial times. Global surface temperature reconstruction suppliers typically reference their anomalies to other more-recent time periods. GISS uses 1951-1980, the UKMO uses 1961-1990 and NOAA often uses 1901-2000, while the WMO recommends 1981-2010. Blogger Rob Honeycutt included that Cowtan-prepared graph in his post The 1C Milestone at SkepticalScience and recommended using pre-industrial times as references for anomalies because it was the best way to convey to persons new to global warming where “we currently are relative to a 2C rise in temperature over preindustrial times”.
Obviously, Cowtan and Honeycutt are overlooking something very important. Their graph shows that it took well over a century for global surface temperatures to reach the 1.0 deg C halfway point. Many newcomers will look at the graph and wonder what all of the hubbub is about.
Cowtan and Honeycutt needed to present something more eye-catching, more alarming, if they were going to get their message across, but they didn’t. The “Halfway to hell” graph was the only graph in the NewScientist article and Honeycutt only added to his blog post a graph of CO2 emissions for different scenarios, which is meaningless to most newbies.
The only way for them to illustrate a fast-approaching threshold would be to present climate model simulations of global surface temperatures. But, oddly, the outputs of climate models don’t appear in those articles.
PRESENTING CLIMATE MODEL OUTPUTS REFERENCED TO PRE-INDUSTRIAL TIMES WOULD LIKELY RAISE SKEPTICISM FROM NEWCOMERS
The time-series graph in Figure 2 includes 81 climate model simulations of global surface temperature anomalies for the period starting in 1880 and ending in 2059, with the modelled global surface temperature anomalies referenced to the pre-industrial times of 1880-1899. Long-term surface temperature reconstructions from GISS and NOAA start in 1880, and 2059 is the year when the last climate model reaches the 2 deg C threshold of imaginary bad things. The models are driven by historic forcings through 2005 and the forcings for the projected worst-case (RCP8.5) scenario starting in 2006. Included are 81 separate climate model runs from a bunch of different modeling groups around the globe. (The listing of the 81 climate models and runs are shown in the legend of the elongated version of Figure 2 here.)
The thing that stands out is the 40-year spread for the time at which climate model simulations of global surface temperature anomalies meet the 2.0 deg C fantasy-based bad-things-might-happen threshold. The slowest model to arrive there does so in 2059 and the quickest model reaches the threshold 5 years from now. Climate models aren’t very helpful when it comes to telling us when we might reach the 2.0 deg C limit.
Maybe that’s why NewScientist and SkepticalScience didn’t present climate models to the newcomers, with the model outputs referenced to pre-industrial times. While it took over a century for observed global surface temperatures to rise 1.0 deg C, the climate models are telling us that the next 1.0 deg C rise will happen in 5 to 44 years. That might be confusing to someone new to global warming. Then somebody like me would have to explain to the newcomers that climate models are not simulating Earth’s climate as it existed in the past, as it exists now, or might exist in the future.
The newcomers might then focus their attentions on 2005, because it was the last year of the hindcast. There appears to be a very large spread in modeled surface temperatures at 2005 when we reference the model outputs to pre-industrial times. And we can confirm that in Figure 3.
So the newcomers to global warming would see that the climate models perform pretty poorly at simulating past global warming. The global temperature anomaly in 2005 from one model is about 1.17 deg C higher than that of another. In other words, there’s a 1.17 deg C spread in the change in simulated global surface temperatures from pre-industrial times to 2005, which is greater than the 1.0 deg C observed rise shown in Kevin Cowtan’s graph (my Figure 1).
And if a newcomer was as curious as I was…and had nothing better to do…she or he just might download all of the 80+ climate model outputs of global surface temperatures with the historic and worst-case RCP8.5 forcings, with the intent of determining the models with the highest and lowest warming rates. Then that newcomer just might compare those models to the warming rate of the alarmist favorite GISS Land-Ocean Temperature Index, with the new NOAA ERSST.v4 pause-buster sea surface temperature reconstruction. See Figure 4. Note that I shifted the GISS LOTI reconstruction and climate model outputs so that the trend lines intersected with zero at 1880.
Figure 4 (I corrected the typo.)
The 0.079 deg C/decade spread in the climate-model-hindcast warming rates from 1880 to 2005 is also greater than the observed warming rate of 0.060 deg C/decade.
ONE LAST POINT
While there’s nothing wrong with presenting the change in temperature as Kevin Cowtan has done (see Figure 1), the climate science community normally relies on linear trends to express changes in a metric over time. Based on the linear trend of the GISS LOTI reconstruction, global surface temperatures have only risen 0.9 deg C since 1880. See Figure 5. It’ll be a while longer (maybe a decade, based on the linear trend from 1880 to 2014) until we reach the halfway mark of the 2 deg C threshold.
Just in case you’re wondering, let’s look at the linear trends of the Berkeley Earth (BEST), the Cowtan and Way, the NOAA NCEI and the UKMO HACRUT4 global surface temperature reconstructions. Only the trend-line value in 2014 of Berkeley Earth comes close to 1.0 deg C. The others show increases (based on their warming rates from 1880 to 2014) that range from 0.9 deg C to 0.85 deg C.
Using pre-industrial times as the bases for anomalies helps to illustrate something very important to persons new to global warming: climate models do a poor job of simulating past global warming. Why then should those newcomers believe the political-agenda-financed climate-model predictions of future global warming that are based on speculations about yet-to-come emissions of greenhouse gases?
The following are links to the data for the long-term global surface temperature reconstructions:
- Berkeley Earth
- Cowtan and Way
- GISS LOTI
- NOAA NCEI (Click on the “Anomalies and Index Data” link)
The climate model outputs are available through the KNMI Climate Explorer.