Posts Tagged ‘solar forcing’

“Believing” in climate change. That’s what it has come to now for a lot of people.

Unlike religion the climate debate does not base it beliefs on faith. The scientific climate debate is not about believers and deniers. There are climate scientists who are proponents of climate change and there are those who are sceptics.

While the overwhelming majority accept that climate change is happening, the real discussion is about whether humans are causing it or not. And instead of just choosing whatever tit bits of information about climate change you heard from a documentary, a pub conversation, or an expert on the news, you could just simply look at the following facts and decide for yourself.

Our earth’s atmosphere is comprised mostly of nitrogen, oxygen and other smaller gases such as water vapour, carbon dioxide and methane. Most of the sun’s radiation passes through these gases because it has a shortwave length. The radiation heats up the ground and is reemitted as longwave radiation – which is the kind of infrared heat you feel from a hot stove or radiator. 

Although these gases allow shortwave radiation to pass through them they absorb the longwave radiation. This causes them to vibrate. And of course vibration is heat.

This heat is radiated throughout the atmosphere by these gases and as a result creates the so called greenhouse effect. Two of these three gases are being produced by human activity – carbon dioxide and methane.

At the Russian Vostok research station in Antarctica an ice core was drilled looking back 420,000 years in time. Using these ice cores climatologists were able to measure both the temperature and the carbon dioxide content of the atmosphere looking back thousands of years.

But interestingly the data showed that the carbon dioxide increases lagged the temperature increases by 800 years. So if carbon dioxide is supposed to cause global warming the lag time would suggest it’s the other way round.

This is where people get a bit carried away without reading the rest of the facts.

There is a trigger that sets off a circle of events, each tipping the earth into a cooling or a warming phase. In scientific terms this circle is called positive feedback.

We know that a similar positive feedback happened during the ice age. When the earth went through a cooling and warming phase it snowballed so that a tiny bit of cooling ended up freezing half the planet and a tiny bit of warming ended up thawing it out again.

But each time something had to act as that initial trigger.

A strong contender has always been regular cyclical deviation in the earth’s position or orbit changing the amount of sunlight the earth received.

Whatever it was during the ice age this change melted a tiny part of the ice sheet and released carbon gasses from the soil and from the warmer oceans. The carbon gasses that were released trapped more longwave radiation and warmed the planet a bit more and that released more carbon gasses and so on.

Climate change proponents have never suggested that carbon dioxide increase was the trigger for past warming, only that the trigger released carbon gasses which set off this vicious circle of heating.

So the lag time isn’t disputed and the reasons for it are part of the global warming model but without a trigger this positive feedback wouldn’t even begin. Luckily the earth’s orbit will remain steady for another 16,000 years.

The problem is anything that causes a tiny increase in temperature can cause this circle of events and the premise of climate change proponents is that our industrial output of carbon dioxide itself is now the trigger.

In Siberia melting ice is thawing out millions of square miles of marsh producing tonnes of methane gas which is a more potent gas than carbon dioxide but much less abundant in the atmosphere. Even so the methane adds to global warming creating more marshland which releases more methane.

The Objections.

One well rehearsed objection is that increased output from the sun is driving climate change, known as solar forcing.

Scientists agree that the earth’s climate warms and cools in concert with the varying energy output of the sun but the question is; is that the cause of the recent rise in global temperatures – over the last 40 or 50 years?

Almost 30 years ago a paper was published with very strong evidence which suggested just that. Eigel Friss-Christensen and K. Lassen of the Danish Meteorological Institute looked at the pattern of solar activity over the last 250 years and it matched almost perfectly with global temperature changes (“Length of the solar cycle: an indicator of solar activity closely associated with climate”).

To get the graph they had to filter the data which involves smoothing it out to account for background variations and local anomalies. This is standard practice and they did this for most of the graph but they didn’t do it for the most recent part of the graph because the data needed to do it wasn’t available at the time of publication.

When it did become available it showed a very good correlation between global temperatures and solar output for most of the last 250 years but not the very period that covers a dramatic rise in global temperatures. While global temperatures have been rising solar activity has been more or less static.

A lot more recent papers also show that solar activity explains most of the temperature changes over the last few hundred years but not the recent period in rising global temperatures.

The bottom line on solar forcing is that a lot of studies have been done and it is not an issue that is being ignored. Output from the sun is an important factor in driving the earth’s climate. But over the last 40 years there has been no significant increase in solar output.

Solar forcing simply doesn’t explain the recent rise in global temperatures.“Variations in solar luminosity and their effect on the earth’s climate”.

Another idea put forward is that cosmic rays seed clouds and when solar activity increases, particles from the sun (i.e the sun’s magnetic field) keep these cosmic rays away from the earth and that reduces cloud cover – Hennrik Svensmark and Eigil Friis-Christensen -“Variation of cosmic ray flux and global cloud coverage: A missing link in solar climate relationships”.

Friis-Christensen and Svensmark provided data that showed a correlation between low atmosphere cloud cover and the intensity of cosmic rays arriving at the earth between 1980 and 1995. But this hypothesis hinges on increased solar output in the last 40 years and this isn’t the case.

So the key point most climate change proponents are trying to get across is that human activity looks like it is the trigger that sets off a circle of events, each tipping the earth into a cooling or a warming phase.

Of course there are so many variables to consider when discussing such a complicated process as the ever changing climate, and each one of us certainly makes a difference whether you want to believe that or not.

But one far too frequently overlooked contributor to climate change, which has huge implications for humanity, is overpopulation, which will be discussed at a later date.