The World is Cooling so the WWF is Turning the Heat On
By Lykke E. Andersen*, La Paz, 27 October 2008.

Last week, WWF came out with an alarming report "Climate Change: Faster, Stronger, Sooner: An overview of the climate science published since the UN IPCC Fourth Assessment Report" suggesting that Global warming is accelerating beyond IPCC's forecasts.

That is a really impressive accomplishment at a time where everything points to the Earth being several years into a cooling cycle (1), probably related to the Sun having suddenly changed from unusually active to unusually quiet (2) and the Pacific Decadal Oscillation having turned into its negative mode (3).

Recent climatic developments notwithstanding, it is theoretically possible that the new research that has come out since the latest IPCC report would suggest that IPCC's model parameters should be adjusted, and that such adjustments would lead to faster, stronger, and sooner warming.   

Only by doing a very selective review, however, could you come to such a conclusion. It is quite easy to do a review which would lead to the opposite conclusion: that warming is going to be weaker and slower and be delayed for several decades compared to IPCC forecasts.

This is no place to do a thorough IPCC-like review of the scientific literature, but we do have space to review a few recent peer-reviewed scientific articles, which would definitely lead to adjustments in the opposite direction of what the WWF report indicates.

One important group of papers suggest that the effect of solar activity is underestimated in the 2007 IPCC models. For example, a 2007 paper in the Journal of Geophysical Research by Scafetta and West (4) finds a very strong correlation between solar activity and temperature over the last 400 years (see Figure 1 below). According to their data sets, the Sun would have explained 42% (+/-20%) of warming since 1950, whereas the IPCC found that the Sun has contributed virtually nothing to the warming since 1950. The paper ends with the following conclusion: “If we assume that the latest temperature and TSI secular reconstructions, WANG2005 and MOBERG05, are accurate, we are forced to conclude that solar changes significantly alter climate, and that the climate system responds relatively slowly to such changes with a time constant between 6 and 12 years. This would suggest that the large-scale computer models of climate could be significantly improved by adding additional Sun-climate coupling mechanisms.”

Figure 1: Solar activity (WANG2005) and Global Temperature Anomalies (MOBERG2005)

Source: Scafetta and West (2007).

There is still room for CO₂ to have an effect on temperatures, but the effect is clearly not as large as if one assumes that the Sun has had only a negligible effect on Global temperature changes since 1950. 

Another paper by Schwarz in the same journal (5) also suggests that the currently used climate sensitivity parameter (how much warming would a doubling of CO₂ cause) is overestimated. His estimations suggest that a doubling of CO₂ would cause the average global temperature to increase by 1.1 +/- 0.5K, which is much smaller than what the IPCC models currently operate with (about 3K). 

Another group of papers attack the temperature records that underlie all analysis and models. McKitrick (2008), for example, find that when properly excluding effects from local land surface modification, the estimated 1980-2002 global average temperature trend over land is reduced by about half (6).

The discussion about the quality of temperature measurements turns even more animated for the longer temperature reconstructions based on proxies, and the question of how warm the Medieval Warm Period was (important if you want to claim that current warming is unprecedented). A very recent paper by Craig Loehle in Journal of Climate Change (7) suggests that trees show a non-linear growth response to temperatures, and that the assumption of linearity (as applied in Mann’s hockey-stick) will create a cold-bias in past temperature reconstructions.

Grudd (2008) reconstructs arctic temperatures based on a modern tree-ring analysis from Torneträsk in the northern part of Sweden (within the Arctic Circle). Here is the key estimated temperature anomaly series from year 500 to 2004 AD:

Figure 2: Reconstructed summer (April–August) temperature for the period AD 500–2004. Panel “a” shows the reconstruction from ring widths exclusively. Panel “b” shows the ‘‘multi-proxy’’ reconstruction from widths and densities. Both series are expressed as anomalies (in °C) from their 1951–1970 mean. The annual data (grey) has been filtered to emphasize climatic variability on 30- and 100-year timescales (black curves). Panel “c” shows the difference on multi-decadal (dark grey) and centennial (light grey) timescales between the two reconstructions (expressed as an in-between fill of the curves), with the ‘‘multiproxy’’ reconstruction showing on average 0.2°C lower temperature estimates. Source: Grudd (2008).

Here is an excerpt from the paper: “The late-twentieth century is not exceptionally warm in the new Torneträsk record: On decadal-to-century timescales, periods around AD 750, 1000, 1400, and 1750 were all equally warm, or warmer. The warmest summers in this new reconstruction occur in a 200-year period centered on AD 1000. A ‘Medieval Warm Period’ is supported by other paleoclimate evidence from northern Fennoscandia, although the new tree-ring evidence from Tornetraäsk suggests that this period was much warmer than previously recognised.” “The new Torneträsk summer temperature reconstruction shows a trend of -0.3°C over the last 1,500 years.”

So, while arctic temperatures have indeed increased during the last century, there doesn’t seem to be anything unusual about this warming. The increase looks a lot like the increase that took place about year 650-750 AD. If you base your climate sensitivity estimation only on the last 100 years (or on the now debunked hockey-stick proxy (8)), you would get a high parameter, but if you use new and more credible proxies for the last 1600 years, you would find little relationship between CO₂ concentrations and Global temperatures.

Nobody knows how long the current cooling cycle is going to last (some say 30 years), but if it lasts just a few more years, then computer models definitely would have to be revised in order to fix the increasing discrepancy between predictions and actual climate. For the purpose of improving climate models, another 10 years of cooling would definitely be a good thing.