Climate change: a real and present danger

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There has been much in the media recently about climate change sceptics, such as Lord Monckton. They challenge the concept that climate change is occurring and that it is caused by humans. JJ Faisson gives the facts.

The Planet is Warming

Globally, we have seen temperatures and sea levels rising faster than expected, with land areas experiencing the fastest increases. Australia has seen an increase of 0.9 ºC since 1950. In fact, our own CSIRO believes that we have observed changes to our climate faster than anything earth as seen for at least 1800 years.

Surface temperature stations have been used since the 1850s, and there are a number of complete records dating back to then. Looking at the diagram on the right, we can see a powerful upward trend from the 1970s onwards. The 2000s were hotter than the 1990s, which were hotter than the 1980s, which were hotter than the 1970s. Indeed, 2010 was declared to be the hottest year on record.

Some of the effects of continued temperature increases are that the sea level continues to rise, the ice sheets continue to retreat, and coral bleaching accelerates. The flow-on effects of these symptoms have the potential to be catastrophic for a large percentage of the world’s population. Australia alone faces massive costs to our environment, including threats to the Great Barrier Reef, Kakadu national park and south-Western Australia. There is also the threat of increased droughts affecting agriculture, as well as impacts on coastal settlements where the sea could move as much as a few hundred metres inland. The cost of such outcomes has the potential to be enormous. See the CSIRO analysis for more details.

Humans are causing this warming

There is overwhelming evidence that humans are the dominant cause of this warming, primarily due to our greenhouse gas emissions. Based on fundamental physics and mathematics, we can quantify the amount of warming human activity is causing, and verify that we’re responsible for essentially all of the global warming over the past 3 decades.  In fact, we expect human greenhouse gas emissions to cause more warming than we’ve thus far seen, due to the thermal inertia of the oceans (the time it takes to heat them).

Science predicts a number of “fingerprints” that we should expect, if current climate change models are correct. Indeed, these have been observed – including more warming at night, more warming at higher latitudes, and upper atmosphere cooling. Furthermore, climate models have projected the ensuing global warming to a high level of accuracy, verifying that we have a good understanding of the fundamental physics behind climate change.

Sometimes people ask “what would it take to falsify the man-made global warming theory?”. Well, basically it would require that our fundamental understanding of physics be wrong, because that’s what the theory is based on. This fundamental physics has been scrutinized through scientific experiments for decades to centuries.

The warming will continue

If we continue to emit large amounts of greenhouse gases, the planet will continue to warm. The models tell us that a doubling of atmospheric CO2 from the pre-industrial level of 280 parts per million by volume (ppmv) to 560 ppmv will cause a rise in the temperature of between 2 to 4.5°C. We’re currently sitting on 390 ppmv, and current predictions show us hitting 560 ppmv at some point between 2050 and 2100 if we do nothing. You might think that a couple of degrees isn’t a very big temperature shift, but keep in mind that the inter-glacial period (125,000 years ago) was 3 to 5 ºC warmer than today and sea levels were 4-6m higher than today). A rise of 1 metre would be enough to displace as much as 10% of the world’s entire population.

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Arguments to the contrary are superficial

Sceptic criticisms of climate science are consistently superficial. For example, the criticisms of James Hansen’s 1988 global warming projections never go beyond “he was wrong”, when in reality it’s important to evaluate what caused the discrepancy between his projections and actual climate changes, and what we can learn from this. And those who argue that “it’s the Sun” fail to comprehend that we understand the major mechanisms by which the Sun influences the global climate, and that they cannot explain the current global warming trend. And those who argue “it’s just a natural cycle” can never seem to identify exactly which natural cycle can explain the current warming, nor can they explain how our understanding of the fundamental climate physics is wrong.

The Big Picture

The big picture is that we know the planet is warming, humans are causing it, there is a substantial risk to continuing on our current path, but we don’t know exactly how large the risk is. However, uncertainty regarding the magnitude of the risk is not an excuse to ignore it. We also know that if we continue on a business-as-usual path, the risk of catastrophic consequences is very high.  In fact, the larger the uncertainty, the greater the potential for the exceptionally high risk scenario to become reality. We need to continue to decrease the uncertainty, but it’s also critical to acknowledge what we know and what questions have been resolved, and that taking no action is not an option.

(This story was originally published on Carbon Tax Facts on July 6, 2011 and has been republished with permission.)

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