View From Down Under

Over that last few years the percentage of Americans who believe in human caused global warming has shrunk, even as the evidence for it has grown.  If the heat and noise of the debate has got you questioning, here is a small sample of the evidence.

First, the things we can know with certainty.

The global climate system has warmed over the last 100 years.  This is unequivocal, and supported by increases in global air and water temperatures, widespread melting of snow and ice, and rising global average sea level.  Yes there are yearly variations around the trend line, and some years are cooler than the previous year, but the trend is real.  (This data comes from NASA Goddard Institute)

The levels of CO2, methane, and nitrous oxide have increased dramatically in the last 100 years.  CO2 levels have increased roughly 35% over the last 50 years.  Methane has increased 48%, and nitrous oxide has increased 18%.  All of these are substantially above the natural range over the last 650,000 years as determined by ice core analysis.

These increases are due primarily to human activity.  Use of fossil fuels, agriculture, and change in land use are the primary contributors to the increase.

The levels of greenhouse gases are highly correlated with increasing global temperatures – and have been for millennia.  The data below comes from analysis of Antarctic ice cores.

These are facts regardless of whether you or I believe them to be facts.

There are other things we can know with a very high degree of certainty.

Climate models have been around for nearly 50 years, and are continuously getting more accurate as more data arrives.  These models are developed both independently and collaboratively by scientists in many countries.  None of these models are able to predict the current increase in global temperatures and sea levels without taking into account the man-made increases in greenhouse gases.  There is a very high degree of certainty that global warming is the result of human activity.

The big unknown is how much more the climate will change in the future.  As you can imagine, this will depend on the level of greenhouse gases we emit.  Estimates for temperature change by the end of this century range from alarming (1.8°C assuming global population peaks mid century and a rapid shift to clean technologies) to catastrophic (4.0°C if economic growth continues to be driven primarily by fossil fuels).

Despite all the certainty surrounding global warming,  the impact of continued climate change on human endeavours is unknown.  Scientists can estimate impacts on sea levels, precipitation, surface temperatures, and more, but calculating the cost of global warming in economic, social, or environmental terms has so far proven to be very difficult.  As has estimating the cost of avoiding further climate change.

But there is no doubt that global warming is real and will continue for some time.