Climate Change Since the Industrial Revolution

Posted on November 24, 2013

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Father Theo goes to climate school 7

Weather changes day-to-day, year-to-year, but beneath this noisy everyday record, climatologists have discovered clear trends in our modern climate.  Temperatures have risen about 0.6o C in the last 50 years, and almost 1o in the past century.  Most of the detected warming has occurred over land and in the north.  Because land is concentrated in the northern hemisphere, the northern hemisphere has experienced more warming than the southern.

Scientists have tracked these changes globally using thermometers since 1880, using satellites since the 1970s.  Climate trends prior to the end of the nineteenth century are measured using proxy data, ice cores, tree rings, the chemistry of deep ocean sediments, and so on.

Manns-hockey-stick

Modern temperature reconstructions like this one Mann et al., combining proxy with instrumental data, show dramatically the late 20th century changes in climate.

The pattern of modern warming, over land rather than over water, is explained by the fact that water is a heat sink.  It has a high capacity for storing heat, and it takes a lot of energy to warm it up.

Go watch a pot and see how much energy it takes to make it boil.

And the oceans are deep.  Heat doesn’t penetrate very far into the soil, but the effects of modern warming have been measured to as deep as two kilometres in the oceans.  Oceans can absorb energy and store it like a battery, and in fact have been doing so.  Most of the surplus energy accumulated during modern day climate change has been stored in the oceans and this has caused the oceans to expand somewhat, resulting in the rise of sea levels.  To date, about half of sea level rise can be attributed to thermal expansion, half to the melting of glaciers and ice sheets.

The melting of glaciers and ice sheets is also attributable to climate change, of course, aided by some positive feedback loops.  For instance, warming creates melt ponds on the tops of Greenland ice sheets which are darker than the underlying ice, and which therefore absorb energy which would otherwise be reflected directly back into space.  This extra energy melts yet more ice.  And so on.

If the Greenland ice sheets melted completely, it would raise sea levels globally by 6 metres.  Antarctica melting would possibly add another 70 metres.  None of that is going to happen soon, but even a one or two metre rise would be catastrophic for some areas.  Some island nations would entirely disappear.  Literally 100s of millions of people would be displaced.

Sea ice melting, which is an ongoing phenomenon, doesn’t contribute to sea level rise because that ice is already in the sea.  But it will and does contribute to warming through albedo effects, because open ocean waters absorb significantly more energy than ice cover does.  At the present rates of shrinkage, in sea ice volume as well as sea ice extent, Arctic sea ice will likely disappear over the summer within a decade or two, and with it Earth’s summer parasol.

All of these changes in climate have been taking place since the beginning of the Industrial Revolution, when humanity started chopping down trees and burning fossil fuels at an accelerating rate.  The proportion of CO2 in the atmosphere has risen from about 315 parts per million (ppm) in the late 1950s to about 395 ppm now.  Methane has also upticked radically along with CO2.  The proportions of greenhouse gases in the atmosphere are presently higher than they’ve been in the last 800,000 years, and, ominously, the changes to the climate are now happening at a breakneck speed.

Time gives everyone and everything a chance to adapt.  The modern rate of climate change is already happening faster than anything the Earth has experienced in many millions of years.  And it’s gaining speed all the time.

The last time the Earth experienced changes this rapid, if the fossil record is anything to go by, we had an extinction event.

You know, like the dinosaurs.

If we don’t do something about our climate soon by halting deforestation and reining in our fossil fuel use (say through a carbon tax) we may well join the dinosaur club.

Credit again to Coursera, UBC and the course Climate Literacy: Navigating Climate Change Conversations, taught by Sarah Burch and Sara Harris.  Any errors are my own. 

Posted in: climate change