 |
 |
| Global Cooling? |
|
|
| Global Cooling? |
Global Dimming
Skeptics of the current global warming sometimes refer to the period between 1940 and 1970. During these years, global temperatures were actually cooling even though greenhouse gases were still increasing. In fact, some of these skeptics point out that scientists were suggesting that another ice age was coming! A few scientists were concerned but there was not a sea-change in thought regarding the possibility of global warming. This period is known as Global Dimming.
Figure 5.1 (Mann, 2009) shows how this global dimming was illustrated in Newsweek Magazine.
As industry ramped up across the globe, much air pollution was being spewed out of smoke stacks along with carbon dioxide. This air pollution was blocking incoming sunlight much like that of a volcanic eruption and had the effect of masking the global warming that was well underway. Once clean air legislation began to pass across the globe, air pollution decreased considerably. Sulfate aerosols have declined significantly since 1970 with the Clean Air Act in the United States and similar policies in Europe. The Clean Air Act was strengthened in 1977 and 1990. According to the EPA (2008), from 1970 to 2005, total emissions of the six principal air pollutants, including particulate matter, dropped by 53% in the US. In 1975, the masked effects of trapped greenhouse gases finally started to emerge and have dominated ever since.
According to Wild, M., Ohmura, A. and Makowski, K. (2007) solar dimming was effective in masking greenhouse warming, but only up to the 1980s, when dimming gradually transformed into brightening. Since then, the uncovered greenhouse effect has revealed its full dimension, as manifested in a rapid temperature rise (+0.38.C/decade over land since mid-1980s). Recent solar brightening cannot supersede the greenhouse effect as main cause of global warming, since land temperatures increased by 0.8.C from 1960 to 2000, even though solar brightening did not fully outweigh solar dimming within this period.
Because of the rapid rate of industrialization of China, India, and other Asian countries in the last few decades, there is still considerable global dimming. If these developing countries pass similar legislation, the rate of global warming will accelerate even faster.
Two important conclusions can be drawn from this data:
Has Global Warming Ended?
Skeptics of the current global warming now refer to the period between 1998 and 2008 and claim that global warming has ended. Some go one step further and claim that global cooling has begun. Of course, the observed data shows that this is nonsense. Figures 5.2 and 5.3 (Sato, 2009) show global temperature changes measured by surface stations and also by satellite. The increasing trend in temperature certainly debunks claims that the world is experiencing global cooling.
According to NOAA climate monitoring chief Deke Arndt (Romm, 2009):
The last 10 years are the warmest 10-year period of the modern record. Even if you analyze the trend during that 10 years, the trend is actually positive, which means warming.According to Schmidt and Wolfe (2009), 19 of the warmest years on record have occurred in the past 25 years. The warmest years globally have been 1998 and 2005 with the years 2002, 2007, and 2003 close behind. The warmest decade has been the last ten years and the warming has been widespread globally. Further signs of this warming trend can be seen in the Northern Hemisphere Sea Ice Extent from the National Snow and Ice Data Center. As the graph in the hyperlink shows, sea ice extent has been dramatically reduced since 1979.
So why do some climate contrarians claim that there is global cooling in the face of this data? It boils down to "cherry-picking" data to intentionally misinform the public. Figure 5.4 (Hausfather, 2008) shows global surface and lower troposphere monthly mean anomalies relative to the 1979-1998 mean temperature. The data is from GISS, HadCRU, RSS, and UAH ranging from January 1979 to February 2008. GISS, HadCRU, RSS, and UAH represent the four organizations that publish online the global average temperature estimates. Many experts believe that GISS data is the preferred set because it is the only set that uses all regions of the globe. HadCRU, RSS, and UAH do not include polar regions.
When one considers monthly mean temperature anomalies from 1998 to 2008 it might “appear” that there is a flat line or global cooling. Keep in mind two important points:
Figure 5.5 (Clark, 2009) focuses on the years 1998 to 2008 which is the time period used by those that wish to deceive the general public into thinking that global cooling is occurring.
Three of the four global average temperatures indeed are decreasing in their trends (although the actual global mean temperatures are still warmer than the previous decades).
Figure 5.6 (Clark, 2009) focuses on the years 1999 to 2009.
Simply by shifting our starting point by one year, all four global average temperatures are increasing in their trends! The point made here is that if one cherry-picks a small subset of the data, one can make just about any claim with a nice plot to back it up. The correct way to view global temperature trends is to look at ALL of the data. Figure 5.7 (Clark, 2009) shows the global average temperatures along with trends from 1880 to present. (Note: UAH and RSS data does not exist before 1980)
It is quite obvious that global temperatures have been increasing since 1880 and at a faster rate in the past two decades.
Much of the heat that is delivered by the sun is stored in the Earth's oceans while only a fraction of this heat is stored in the atmosphere. Therefore, a change in the heat stored in the ocean is a better indicator of climate change than changes in atmospheric heat. Figures 7.2 and 7.3 (Richardson et al., 2009) displayed on my Modern Day Climate Change page clearly show that the oceans have warmed significantly in recent years and the trend is 50% greater than that reported by the IPCC in 2007. There is certainly no global cooling in the oceans!
If you prefer to watch a video explaining much of what appears on this Web page, please watch 1998 Revisited from Peter Sinclair's Climate Denial Crock of the Week series on YouTube.
Here is a more technical analysis of why global temperatures have not "cooled since 1998" nor "cooled since 2001" as some global warming critics claim: Embarrassing Questions from the Open Mind Blog.
Next: Climate Models & Accuracy
Last updated: 10/26/09
