ExClimate: CO2 Passing 400 parts per million, a comparison with the Pliocene

The Pliocene period, 3 to 5.3 million years ago, was the last time CO2 was at 400ppm. Investigate what the temperatures were during this time period and compare them to today. Using your knowledge from the course so far, what could explain the changes?

2013 was the first time planet Earth passed 400ppm carbon dioxide in the atmosphere since the Pliocene perod. Instruments at the Mauna Loa Observatory in Hawaii have been measuring atmospheric CO2 and other greenhouse gases for over 50 years. Other sites like CSIRO's Cape Grim observatory in Tasmania and New Zealand's National Institute of Water and Atmospheric Research (NIWA) at Baring Head Station near Wellington also take baseline measurements of atmospheric greenhouse gases.

The Keeling curve shows the rising levels of atmospheric carbon dioxide trend and is one of the most well known climate graphs. It was named after Charles Keeling from the Scripps Institute for Oceanography who started measuring CO2 at Mauna Loa in 1958 and continued up to his death in 2005. The graph clearly shows the northern hemisphere season cycle of carbon dioxide as part of the biological seasonal processes as CO2 is taken up by vegetation in Spring and Summer, then expired in Autumn and Winter, but the long term trend has been a gradual rising of CO2 by about 2ppm per year.

The significance of reaching 400ppm is that the planet has not seen this level of carbon dioxide for 3 to 5 million years, in the Pliocene Period. It was a warmer world then. By examining this geological period we can gain some insight on what we might expect to happen to temperatures, sea levels, the impact on ice sheets, and some signs of how our climate might change later this century and further into the future.

ExClimate: The Ice Albedo Feedback mechanism and Snowball earth

This article is a little bit of a tangent to my regular articles. I am presently doing an online course - Climate Change: Challenges and solutions - offered by the University of Exeter (UK). So please indulge me as I also use this blog for some climate course work. This article is for section 2.3 of the course on Snowball earth events that have ocurred in the distant past.

No one is sure what precipitated the onset of snowball earth events. The oldest snowball earth event occurred approximately 2200 million years ago. The most recent event ended about 635 million years ago and is thought to have lasted 6 to 12 million years. Very basic life managed to survive at least the most recent snowball earth event.

The earth's orbit around the sun, it's axial tilt, and wobble all have different millenial cycles which can affect the amount of solar radiation being absorbed by the earth. Earth’s orbit changes from near circular to oval shape on a 100,000-year cycle (eccentricity). Earth’s axis is tilted and is presently at 23.5 degrees. It varies between 21.5 and 24.5 degrees every 41,000 years (obliquity - Milankovitch cycles). As the Earth spins it wobbles on its axis toward and away from the Sun over the span of 19,000 to 23,000 years (precession).

What caused the earth to go into a giant snowball is still being debated in scientific circles. A number of theories have been advanced including :

• a reduction in solar output,
  
• the Earth passing through rare space clouds,
  
• a combination of high obliquity in the Earth's orbit, orbital eccentricity or precession;
  
• Lithospheric weathering reducing atmospheric carbon causing planetary cooling
  

Ice Sheets and Sea level: what the past tells us is likely.

Watch this informative video By Peter Sinclair and the Yale Forum on Climate Change and the Media on ice sheet collapse and sea level rise and past climates.

"We are still potentially underestimating the instability of the ice sheets" informs Stefen Rahmstorf, Professor of Physics of the oceans from Postdam University. "The IPCC has greatly revised it's estimates of how unstable the Greenland ice sheet was"

Dr Richard Alley in a graph illuminates that on current CO2 levels we can expect sea level rise to impact 10 per cent of the Earth's population, hundreds of millions of people. He says in the video that "Greenland is very tightly tied to temperature, and if it gets too hot, it goes away".

Changes in extent and intensity of wildfire linked to Climate change

A new international scientific study lead by a researcher from the University of Utah links extreme fire weather to increasing temperatures and drought driven by climate change.

The study, lead by geography professor Mitchell Power, found that the extent and intensity of wildfires on a continental and global basis is connected to changing temperatures and climate. The study dismissed the theory that population decline was the primary cause for reduced wildfire during the cooler periods in the last 2000 years arguing "climate change was likely more important than indigenous population collapse in driving this decline."

Global Warming means 20 Metre sea level rise in the pipeline say scientists

Scientists studying the geological record have determined that at slightly above current temperatures we are about 20 metres below what the sea level equilibrium should be. Sea levels are increasing and forecast to rise at least a metre this century (although there is a low probability they could be higher than this), much of the change in sea level will occur over several hundred or thousands of years.

Scientists looking at the Pliocene period from 2.7 to 3.2 million years ago, the last time temperatures were at a similar range of 2 degrees C above average, estimated peak sea level was 22 ± 10 m higher than modern levels (extreme likelihood). This rise in sea level would require the equivalent of the Greenland and West Antarctic ice sheets disintegrating, and some volume loss from the East Antarctic Ice Sheet. We are already seeing substantial mass loss from Greenland and West Antarctic Ice sheets.

Related: Scientists Estimate Sea level Rise for next 500 years | Sea Level Rise and Australia | Video Interview - The risks of Sea Level Change - Dr Peter Ward

Climate sensitivity - paleoclimate record points towards potential rapid climate change

"The paleoclimate record reveals a more sensitive climate than thought, even as of a few years ago. Limiting human-caused warming to 2 degrees is not sufficient," said NASA climatologist James Hansen at the American Geophysical Union meeting on December 6 2011, "It would be a prescription for disaster."

In a press conference at the American Geophysical Union Fall meeting 2011 in San Fransisco climate scientists James Hansen, Ken Caldeira and Eelco Rohling explained that the climate sensitivity may be greater than previously thought. This has implications particularly for action on climate change mitigation and adaptation with major impacts on sea level rise, ocean acidification and many other areas. The latest proposals and pledges from Durban put the world on the path of 4.3°C of warming by the end of the century.