We now know what we don't know about climate change
The Ottawa Citizen
Monday, December 12, 2005
Page Name: Arguments
Byline: Professor Tad Murty
Source: Citizen Special
Over the last 15 years more than $40 billion has been spent worldwide on climate change research, yet the role of humans in the past century's modest warming remains controversial. In fact, the mysteries of climate change have deepened, if anything.
How can the science behind global warming still be so unsettled? The scientific question is deceptively simple. Do rising levels of greenhouse gases such as carbon dioxide (CO2) explain global warming, or is it a natural phenomenon?
To read newspapers or listen to TV and radio, you would think it was all very straightforward -- CO2 levels have risen and so has the global temperature. But this simple story is clearly false.
While it is true that atmospheric CO2 has risen steadily for the last 100 years or so, temperature has not. In fact, as best we can determine, global temperatures fell during the middle half of the last century, while CO2 climbed steadily. Even worse, some parts of the Earth have cooled over the entire last century. So the simple theory -- CO2 up, temperature up -- is unsubstantiated.
The necessary correlation is not there. Other factors must be involved, and it is the search for these causes that has turned climate-change science into a $40-billion puzzle. As always in unsettled science, there are many theories, with much controversy.
Those who believe that humans are causing significant global warming argue that volcanoes may have masked the warming during the 20th-century's cooling period, while natural regional variability explains local cooling.
Those who disagree argue that natural variability has caused both the warming and the cooling. They say the Earth was warm several hundred years ago, then generally cooled for several centuries until around 1850, then started warming again, not smoothly, mind you, but in fits and starts. Variability in the sun's energy is often cited as the cause, and there are some very good correlations to back this up.
Changes in ocean circulation is another prominent theory. But nothing is settled and each new study pulls in another direction.
However, there is one thing we know for certain as a result of all this research, and that is that climate is never constant. We also know that it is extremely complicated, far more so than we imagined just 15 years ago. It is this natural variability and complexity that has made it so difficult to figure out what role humans play, if any.
What started out as a simple question has turned into one of the biggest scientific puzzles of all time. While this is frustrating to people who want easy answers, it is great science.
Adding to the confusion are the computer models. These are basically enormous computer games, called simulations. Each game, and there are many, starts with a version of the Earth's climate system. This may include the atmosphere, clouds, oceans, polar ice caps, sun, forests and humans, each represented in myriad different ways.
Each model of climate is like a fortress within which an endless series of scenarios can be played out. Given a basic game, one can try different factors to see what happens. People use these climate games to try to figure out why the temperature has gone up and down, and up again, and what it might do in the future. Extreme scenarios are often used, to try to make the effect of a given factor stand out.
For example, in the last 150 years the CO2 level has increased by about 30 per cent, but modellers look at future increases of 300 per cent or more, 10 times reality.
Unfortunately the results of playing these climate computer games with extreme scenarios are often reported in the media as facts about the Earth and our future climate. The reality is that, as with any computer game, a great deal is possible that is not realistic. This is especially true given that we really do not understand why the climate is behaving as it is. We do not know why the Earth has warmed and cooled, so we cannot predict the future. We do not know which game to believe.
For example, some extreme scenarios have the vast Greenland and Antarctic ice caps melting, flooding the world's coastal cities. Many people believe this is actually happening, based on alarmist headlines.
The reality, determined by extensive measurements, suggests that both ice caps are growing in volume, not shrinking. In a paper titled "Snowfall-driven growth in East Antarctic ice sheet mitigates recent sea-level rise," published in May 2005 in the prestigious journal Science, researchers Davis et al used satellite measurements to show that parts of the East Antarctic ice sheet increased in mass by about 45 billion tons per year from 1992 to 2003. Also not appreciated by the general public is the fact that the South Pole itself is colder now than at any time since record keeping began in the International Geophysical Year, 1957.
It turns out that our planet -- and therefore the science that attempts to describe it -- is immensely more complicated than Kyoto supporters suggest. Forty billion dollars buys a lot of science, and that science is paying off. We now understand the complexity and natural variability of climate in ways that were unimaginable just 10 years ago.
But the price of this understanding is that we now know that we do not know why the Earth is warming. We do not know if humans have anything to do with it, and they may well not. The scientific assumption behind the Kyoto protocol, namely that humans are known to be significantly interfering with an otherwise unchanging climate, is simply false. A new era of climate science lies before us.
Dr. Tad Murty is a former senior research scientist with Fisheries and Oceans Canada and director of Australia's National Tidal Facility. He is currently an adjunct professor in civil engineering and earth sciences at the University of Ottawa and an editor for the international scientific journal Natural Hazards.
Note: After giving the key note address at the 42nd annual conference of the Indian Geophysical Union (IGU) last week, Professor Murty received the IGU Gold Medal in Oceanography. He may be contacted at email@example.com