Wednesday, June 28, 2017

We Are Heading for the Warmest Climate in Half a Billion Years, Says New Study

Man walkig camels in desert (Credit: http://total-management.com) Click to Enlarge.
Carbon dioxide concentrations are heading towards values not seen in the past 200m years.  The sun has also been gradually getting stronger over time.  Put together, these facts mean the climate may be heading towards warmth not seen in the past half a billion years.

A lot has happened on Earth since 500,000,000BC – continents, oceans and mountain ranges have come and gone, and complex life has evolved and moved from the oceans onto the land and into the air.  Most of these changes occur on very long timescales of millions of years or more. However, over the past 150 years global temperatures have increased by about 1℃, ice caps and glaciers have retreated, polar sea-ice has melted, and sea levels have risen.

Some will point out that Earth’s climate has undergone similar changes before.  So what’s the big deal?

Scientists can seek to understand past climates by looking at the evidence locked away in rocks, sediments and fossils.  What this tells us is that yes, the climate has changed in the past, but the current speed of change is highly unusual.  For instance, carbon dioxide hasn’t been added to the atmosphere as rapidly as today for at least the past 66m years.

In fact, if we continue on our current path and exploit all convention fossil fuels, then as well as the rate of CO₂ emissions, the absolute climate warming is also likely to be unprecedented in at least the past 420m years.  That’s according to a new study we have published in Nature Communications.
...
So high concentrations of carbon dioxide don’t necessarily make the world totally uninhabitable.  The dinosaurs thrived, after all.

That doesn’t mean this is no big deal, however.  For a start, there is no doubt that humanity will face major socio-economic challenges dealing with the dramatic and rapid climate change that will result from the rapid rise to 2,000 or more ppm.

But our new study also shows that the same carbon concentrations will cause more warming in future than in previous periods of high carbon dioxide. This is because the Earth’s temperature does not just depend on the level of CO₂ (or other greenhouse gases) in the atmosphere.  All our energy ultimately comes from the sun, and due to the way the sun generates energy through nuclear fusion of hydrogen into helium, its brightness has increased over time.  Four and a half billion years ago when the Earth was young the sun was around 30% less bright.

So what really matters is the combined effect of the sun’s changing strength and the varying greenhouse effect.  Looking through geological history we generally found that as the sun became stronger through time, atmospheric CO₂ gradually decreased, so both changes cancelled each other out on average.

But what about in the future?  We found no past time period when the drivers of climate, or climate forcing, was as high as it will be in the future if we burn all the readily available fossil fuel.  Nothing like it has been recorded in the rock record for at least 420m years.

Read more at We Are Heading for the Warmest Climate in Half a Billion Years, Says New Study

No comments:

Post a Comment