This is a reply to a Dutch article which quotes Fred Singer as claiming that CO2 has hardly any effect on climate; that climate change is due to the sun; that global warming stopped in 1998; and that sealevel won’t rise faster than it has done in the past thousands of years. I wrote the following reply.
(Nederlandse versie hier.)
The premise that CO2 has hardly any influence on climate, as argued by Fred Singer, can not be sustained. These so-called “critical” opinions may fare well in the media, but in the current scientific debate they don’t play any role. They have been proven wrong long ago.
The current media don’t pay much attention anymore to claims that smoking wouldn’t have adverse health effects (something Singer argued in the past). Or to claims that CFC’s wouldn’t destroy the ozone layer (Singer also argued that, until just before the Nobel Prize for Chemistry was awarded to those who showed that they do). It’s about time that the media also start portraying climate change in line with current scientific knowledge.
CO2 and global warming: hypothesis or fact?
It has been known for over 100 years that CO2 absorbs infrared radiation, and thus has a warming effect. This effect causes the Earth to have a hospitable climate, and Venus to be boiling hot. Of course there are uncertainties in climate science, but our knowledge has definitely progressed a few stations beyond what Singer and a handful of other (ex-) scientists claim.
The observed change in temperature over the past 100 years is reasonably well reproduced by climate models. The past 10 years do not change that picture, although it has to be noted that temperature changes over a decade (or less) are heavily influenced by the changeable weather, large volcanoes and the El Niño (1998) / La Niña (2007) cycle.
There are a few things that are now beyond reasonable doubt:
- Global climate has warmed over the past ~100 years, with the largest increase in temperature from about 1975.
- The concentration of CO2 and other greenhouse gases has increased due to human activity.
- Basic physics and numerous observations point to a causal relationship.
- Further increase in greenhouse gas emissions will lead to further warming.
Of course there are other factors besides greenhouse gases that can influence the climate, such as aerosols, land use, solar activity, etc. The sun is often put forward by “skeptics” as being the main reason for the current warming. But although the increase in solar activity in the first half of the 20th century indeed contributed to the warming, the solar activity (and related quantities such as cosmic rays) has remained more or less constant since the sixties. The strong increase in temperature from 1975 onwards can therefore not be explained by varying output of the sun.
An alternative explanation of current climate change can not just put aside the accumulated body of knowledge and observations; they have to be integrated into a total picture. The infrared absorbing ability of greenhouse gases can not just be denied by pointing to the sun. You don’t deny gravity either when you see a bird fly.
Sea level rise
Sea level is rising faster than it has in the past (before 1900), and also faster than predicted by climate models. The possibility of (mechanically) enhanced melt of land ice is an active research area where knowledge is still lacking. But this uncertainty should not be a comfort, because the risks of a substantial sea level rise are large. Many of the large population centers are located in the vicinity of the sea at only small elevation.
Singers unfounded opinion about CO2 is not relevant for the discussion about energy options, just as his opinion about smoking is not relevant for the discussion of anti-smoking laws. About policy options, for example concerning energy, there will always be different opinions. And different opinions should be heard. But please leave out scientifically proven untruths. They don’t contribute to the debate. To the contrary.