Happy 2050

The best estimate from the IPCC is that the global average temperature of the earth’s surface has increased a 0.6ºC (+/- 0.2ºC) over the last 100 years.

When the objection is raised that this past increase is a natural phenomenon – as opposed to the consequence of human greenhouse gases’ emissions – the implicit foregone conclusion is that mankind is off the hook.

The truth is that one does not exclude the other. If nature is a factor, then both natural variability and the increase of greenhouse gases’ concentration in the troposphere will have cumulative effect in future temperature rise – making climate change an even bigger crisis.

Before we worry sick(er) about a double whammy effect, is there evidence that rules out natural variability as a factor in past warming?

Evidence #1

The IPCC report shows the following variation of the earth’s surface temperature for the past 1,000 years and for the past 140 years

Source: http://www.ipcc.ch/ipccreports/tar/vol4/english/pdf/wg1spm.pdf

The rise over the 20^th century is visible and represents a clear break from a previous stable to mild-cooling trend. But the magnitude of the recent increase is in the error range of older temperature measurements. So no definitive answer can be drawn from these graphs only.

Evidence #2

Since the rise after 1970 is pretty steep, let’s look for any major change to the natural factors that influence our climate during that same time period.

• No noticeable changes were observed for volcanoes’ activities.
• For solar radiation, the story is more convoluted. In the mid-70s, scientists noticed that the rate of evaporation was dropping, although you’d expect it to increase with global warming. Scientists were stunned to discover that the sun had actually been growing dimmer with less and less sunlight reaching earth’s surface. This had likely been caused by an increase in particles like aerosols in the atmosphere, due to human activities. This trend switched in the 90s, just as global aerosol levels started to decline.

If anything, global dimming created a cooling effect that may have partially masked the effect of greenhouse gases on global warming.

Evidence #3

Temperatures have risen more quickly during the night and winter, than during the day and summer in temperate countries.

The greenhouse effect is constant throughout the day: it “blocks” terrestrial radiation with the same intensity all day long. On the other hand, solar heating is null at night and lower in the winter. So the greenhouse effect has a bigger influence on temperatures when there is no sun, i.e. at night and in the winter.

The observed pattern is therefore consistent with the additional greenhouse effect human emissions have generated.

Evidence #4

In its 2001 report, the IPCC stated that no climate model could reproduce the temperature rise of the second half of the 20^th century without factoring in anthropogenic greenhouse gases emissions.

The inescapable conclusion to all of this? Natural phenomenon or not, we need to change our current ways of doing business and living our lives. Go & check towards a happy 2050 to determine how worried we should be!

This entry was posted Wednesday, February 4th, 2009 at 10:27 pm and is filed under Climate change. You can leave a response, or trackback from your own site.