Kate McIlwain

Climate change is real, believe me

By Dr Helen McGregor*

As a climate scientist I am often asked if I believe in human-induced climate change. I find this a curious question: for me the science of human-induced climate change is not something one believes in but an obvious conclusion drawn from the data. But it got me thinking – where has this belief/non-belief idea come from and why is there so much confusion about climate science?

There is no doubt that climate is a complicated beast. There are multiple players – the main ones being the atmosphere, ocean, vegetation, and ice – all of which interact with each other on a variety of timescales from hours to decades to centuries and beyond. Trying to describe all the processes, and to put them in a climate model, is a tough gig. But it can and has been done. Our daily weather forecasts are based on models, and though not perfect, they’re often within a couple of degrees Celsius of the actual temperature. That’s quite an achievement when you think about it.

Importantly, the models reproduce the observed 20th Century warming. This means that at least at the global scale we do have a good handle on the climate complexity. But communicating this complexity to the public is no mean feat and scientists aren’t always the best at communicating their own science in a language that non-scientists can understand.

One of the difficulties in communicating climate science is the concept of “uncertainty”. With the vast number of processes in the climate system there are some that we understand better than others - uncertainty describes how well we know what we know. Climate scientists, having a good understanding of uncertainty, tend to downplay the state of knowledge and this can be taken by some as a reason to do nothing.

But there are many instances where we may not understand a process 100 per cent still act. For example, we know that a healthy diet and exercise reduces the risk of heart disease, yet the details of exactly which food and how much exercise are still the subject of research. Does this mean we should have an unhealthy diet and not exercise? Of course not. The same principle applies to reducing carbon dioxide (CO2) emissions. We know that there is a big problem and should get on with the process of dealing with it.

The concept of uncertainty and the complexity of climate science also do not sit comfortably with the demand from the media for short “sound bites”, a black and white statement, one view for and one view against. Uncertainty is the greyness around the black and white. The for and against may appear to give balance but it misrepresents the almost absolute consensus among climate scientists – 97-98 per cent consensus according to findings published this month in the USA Proceedings of the National Academy of Sciences – and provides a louder voice to those who disagree with the idea of human-induced climate change than they would otherwise deserve.

Throw into this mix various lobby groups and vested interests in maintaining the status quo and the concept of uncertainty can be exploited further to confuse the public. In responding to human-induced climate change we move through climate science into economics, politics and social sciences. Between all of this it seems to become easier to frame the debate as a question of belief or non-belief. The understanding of how the science is generated and its implications are lost, and somehow by non-believing the problem does not exist.

But the issue of human-induced climate change is clear and present, and among all the confusion there are some fundamentals that will not change, and some misconceptions that must be addressed:

  • Carbon dioxide in the atmosphere traps heat and this causes the atmosphere, and the planet, to warm.
  • The burning of fossil fuels has increased the level of CO2 in the atmosphere. This has been measured directly at places like Mauna Loa in Hawaii and by measuring bubbles of trapped air in ice cores. CO2 levels have increased from 280 parts per million (ppm) at around 1800 to 385 ppm in the past couple of years. As a result the planet is about 0.7 degrees Celsius warmer. This doesn’t sound like much but there are knock-on effects from the temperature increase. Ocean water has warmed, and water expands when it’s warmer, so sea levels have risen. The warming is not distributed evenly across the world because the poles have warmed the most, so sea ice is retreating and the ice sheets have started to melt. Sea ice is important – it’s like a giant mirror reflecting the sun’s heat and light back out into space. Without the sea ice that heat is absorbed by the ocean, further warming the planet.
  • The atmosphere, winds and the like, redistribute CO2 across the planet in a matter of months so that even though the US and China are the biggest emitters of CO2, those countries do not feel the full force of their own emissions. Hence global warming is a global issue.
  • Australia is part of the CO2 problem. I often hear the argument, including from politicians, that Australia only emits about 1.5 per cent of the global total of CO2. Quite so, however 95 per cent of countries emit less than 2 per cent of the global total. It is not possible for countries to do nothing – Australia must reduce its CO2 emissions. Period.

As I sit here in bustling New York City, with the gulf oil spill making headline news day in day out, I can’t help but be anxious that climate change issues have slid under the radar. Human-induced climate change is insidious. It is not an acute, headline-grabbing event but the consequences of climate change will have far greater and far reaching impacts. The science provides the clear evidence that human-induced climate change is occurring – the real uncertainty lies in our collective ability to do something about it.

*Dr Helen McGregor, School of Earth and Environmental Sciences, is currently visiting the Lamont-Doherty Earth Observatory, University of Columbia, New York. Upon her return Dr McGregor will be teaching in the Faculty of Science’s Climate Change subject.