Global Warming and Measuring GDP

GDP is a statistic and is subject to measurement error.  Economists have long recognized that pollution harms resources and economic activity and that the lost value should be subtracted from GDP, but this is a difficult and costly practice.  Anthropogenic global warming offers an example of the problems researchers would encounter measuring pollution cost.  The first problem is to measure the portion of the recent increase in temperatures due to nature and man.  Paul Hudson of  BBCNews describes the fight in the scientific community over the causes of climate change in "What happened to global warming?" 

This headline may come as a bit of a surprise, so too might that fact that the warmest year recorded globally was not in 2008 or 2007, but in 1998.

But it is true. For the last 11 years we have not observed any increase in global temperatures.

And our climate models did not forecast it, even though man-made carbon dioxide, the gas thought to be responsible for warming our planet, has continued to rise...

Note the error in the next quote which refers to "climate change skeptics."  As the author notes in the ensuing paragraphs, some skeptics believe that climate change is predictable by measuring solar output and presumably, not carbon emissions.  The quote should begin, "anthropogenic climate change skeptics." 

Climate change sceptics, who passionately and consistently argue that man's influence on our climate is overstated, say they saw it coming.

They argue that there are natural cycles, over which we have no control, that dictate how warm the planet is. But what is the evidence for this?

During the last few decades of the 20th Century, our planet did warm quickly.

Sceptics argue that the warming we observed was down to the energy from the Sun increasing. After all 98% of the Earth's warmth comes from the Sun...

Other sceptics look to the oceans as drivers of climate change.

The oceans, he [Professor Easterbrook] says, have a cycle in which they warm and cool cyclically. The most important one is the Pacific decadal oscillation (PDO).

For much of the 1980s and 1990s, it was in a positive cycle, that means warmer than average. And observations have revealed that global temperatures were warm too.

But in the last few years it has been losing its warmth and has recently started to cool down.

These cycles in the past have lasted for nearly 30 years.

So could global temperatures follow? The global cooling from 1945 to 1977 coincided with one of these cold Pacific cycles.

Professor Easterbrook says: "The PDO cool mode has replaced the warm mode in the Pacific Ocean, virtually assuring us of about 30 years of global cooling."

Scientists that support theories of anthropogenic global warming caused by carbon emissions don't agree with the theories that the sun or oceans are driving recent climate change.

The UK Met Office's Hadley Centre, responsible for future climate predictions, says it incorporates solar variation and ocean cycles into its climate models, and that they are nothing new.

In fact, the centre says they are just two of the whole host of known factors that influence global temperatures - all of which are accounted for by its models.

In addition, say Met Office scientists, temperatures have never increased in a straight line, and there will always be periods of slower warming, or even temporary cooling.

What is crucial, they say, is the long-term trend in global temperatures. And that, according to the Met office data, is clearly up.

After deciding if the earth is warming or cooling and man's contribution to the change, scientists must determine if the change is good or bad for economic activity.  The answer is clear that small increases in temperature have aided human development.  Henrik Svensmark gives a one paragraph summary of 1,000 years of climate variation on economic activity in "While the sun sleeps by Henrik Svensmark."

Solar activity has always varied. Around the year 1000, we had a period of very high solar activity, which coincided with the medieval warmth. It was a period when frosts in May was an almost unknown phenomenon and of great importance for a good harvest. Vikings settled in Greenland and explored the coast of North America. For example, China’s population doubled over this period. But after about 1300, the earth began to get colder and it was the beginning of the period we now call the Little Ice Age. In this cold period all the Viking settlements in Greenland disappeared. Swedes [were surprised to see Denmark to freeze over in ice], and the Thames in London froze repeatedly. But more serious was the long periods of crop failure, which resulted in a poorly nourished population, because of disease and hunger [population was reduced] by about 30 per cent in Europe.

Without reference, other scientists believe that anthropogenic climate change from carbon emissions will cause more warming than experienced in the past and that it will lead to large declines in economic activity. 

Economists would have difficulty measuring the impact of anthropogenic climate change on the economy.  I understand why it is not attempted.