The Warming Earth - What share of warming is caused by human activity, and what is the risk?

What share of climate change is caused by human activity?
Scientists at the Geological Society of London say -
How has this been discovered?
The key is found in looking at the evidence of the Ice Age.
The 'Ice Age' is actually a long set of colder (glacial) stages and warmer (interglacial) stages.
The last major glacial stage of the "Ice Age" ended thousands of years ago.

 Since the ice melted back, the temperature has changed, but the recent rise is very different.
The graph shows that after the ice melted, temperatures continued to rise for a few thousand years.
Around 10,000 years ago the global temperature steadied (with some 'wiggles') until about 5,000 years ago.
Then the Earth began to slowly cool, and that continued until modern times, with some variations.
So left to itself the Earth would be cooling towards a new glacial stage.


Glacial stages are linked to regular patterns in the movements of the Earth.

















The ice would start to return in around 1,500 years.

So the current rise in temperatures is not part of a natural cycle.



The natural cooling trend has been reversed.

This temperature rise is the effect of extra carbon dioxide.

The carbon dioxide has been produced mainly by burning fossil fuels.

(In the graph, Law Dome is a site in Antarctica where ice cores have been drilled to discover the ancient CO2 values - Mauna Loa is a site in Hawaii where the CO2 value has been measured in the air since the 1950s)

Popular posts from this blog

Climate Change - The link with mass extinctions

Image
What is the worst-case scenario for climate change? The geological record shows that when the atmosphere suddenly changes, there are big effects on living things. Five major  mass extinction  events are recorded in the rock record of the last 600 million years. The biggest extinction was at the end of the  Permian , around 252 million years ago. It is called the  End-Permian mass extinction. Only about 8% of species survived to live on in the Triassic Period. This photo shows geologists investigating tilted sedimentary rocks at Shangsi in South China. Triassic rocks (at the top right) lie over the older Permian rocks. Each mass extinction in the rocks matches with a change in the chemistry of the rocks called a ' carbon excursion '. Some of the carbon excursions are 'negative CEs' and some are 'positive CEs'. Negative CEs  indicate that lots of gaseous carbon compounds escaped into the air, causing warming. These are sometime
Read more

Climate Change - The Greenhouse Effect

Image
What do scientists mean by the " Greenhouse Effect "? When the Sun's energy arrives at the Earth, it travels through the air. Some is reflected back to space, but some hits the Earth and warms it. The warm Earth gives off  infrared radiation  with various wavelengths.   Some of those waves can pass back out of the air to space, but some are absorbed by certain gases in the air. The gases then re-emit the energy into the air. If there are more of those gases, less heat escapes into space. An extreme case has happened on Venus. Concentrated  'greenhouse gases'  on Venus have caused the surface temperature to rise to 735  Kelvin  (462 degrees C; around 900 degrees F) Carbon dioxide levels in the atmosphere have risen quickly  since people began burning large quantities of fossil fuels. There was carbon dioxide in the air before that, at around 270 parts per million. Without any carbon dioxide, the Earth would be very cold.
Read more

Climate Change - Coal and carbon dioxide

Image
Coal, oil and natural gas are  fossil fuels . When they are burned, they  change the Earth's atmosphere. How is that possible?       C oal  is a good example. Coal was formed  hundreds of millions of years ago . Geologists say that a three-metre (10-foot) coal seam took between  12,000 and 60,000 years  to form . Ancient trees and other plants lived, died and were fossilised. All those plants took  carbon dioxide  out of the atmosphere.  Some larger coal seams are, for example, 10 metres thick. They took around  40,000 years to form,  but have been mined and burned in a little over  100 years. The fastest rise of CO 2  in the air seen in   the ice core record (800,000 years)  is  20 ppm in 1000 years. The CO 2  level in the atmosphere is now rising at around  20 ppm per decade . The  carbon  joins up with  oxygen  when it burns. Each carbon atom joins with two oxygen atoms to make a  carbon dioxide molecule .  As a result, oxygen concentration i
Read more