James Hansen, Goddard Institute for Space
Studies, NASA
• Long-term feedback systems more powerful than
thought previously
• Amplification – albedo, methane, warmer seas
• Earth’s climate sensitivity about twice as much as we
thought – not 3 degrees, but more like 6.
Back to the ice….and its cousin, the
permafrost….
“The thaw and decay of permafrost carbon is irreversible.”
Methane is 25 times as potent a heat-trapping gas as CO2 over a 100 year
time horizon, but 72 times as potent over 20 years .
Yet, no climate model currently incorporates
the amplifying feedback from methane
released by a defrosting tundra.
The carbon comes from plant material frozen in soil during the ice age of the Pleistocene:
the icy soil trapped and preserved the biomass for thousands of years. Schaefer equates
the mechanism to storing broccoli in the home freezer: “As long as it stays frozen, it stays
stable for many years,” he said. “But you take it out of the freezer and it will thaw out and
decay.”
They found that between 29-59 percent of the permafrost will disappear by 2200. That
permafrost took tens of thousands of years to form, but will melt in less than 200 .
Photo: melting permafrost, Alaska
Also like fossil fuels, the PCF is irreversible: once the permafrost carbon
thaws and decays, no process on human time scales can put the carbon
back into the permafrost.
Thawing permafrost feedback will turn Arctic from carbon sink to source in
the 2020s, releasing 100 billion tons of carbon by 2100 (National Snow
and Ice Data Centre (NSIDC) 2011),
“Release of even a fraction of the methane stored in the shelf could
trigger abrupt climate warming.”Methane and carbon release from the
Arctic is the most dangerous amplifying feedback in the entire carbon
cycle. This research finds a key “lid” on “the large sub-sea permafrost
carbon reservoir” near Eastern Siberia “is clearly perforated, and
sedimentary CH4 [methane] is escaping to the atmosphere.”
Planetary temperature over the last 65 million years…
Lessons for today… and tomorrow.
Eocene
peak
This is a graphical interpretation by David Spratt, Melbourne Climate Action Centre,
of aspects of recent paleoclimate research by Hansen et al, available in draft form at:
http://arxiv.org/abs/1105.1140
http://www.columbia.edu/~jeh1/mailings/2011/20110118_MilankovicPaper.pdf
http://www.columbia.edu/~jeh1/mailings/2011/20110514_PaleoAndImbalance.pdf
Version 1.2 of 3 June 2011
Antarctic glaciation ~ 34 million years ago…
Eocene
peak
Around 34 million years
ago, glaciation of
Antarctica as temperature
drops from Eocene peak.
Asteroid impact cluster
(~35mya): opening of
Drake Passage leads to
the circum Antarctic cold
current
Northern hemisphere glaciation ~ 4.5 million years ago…
Eocene
peak
Around ~4.5 million years ago, northern hemisphere glaciation.
Associated with the rise of the Panama Cordillera which isolates
the Pacific from the Atlantic oceans and leads to intra-oceanic
circulation (Gyres) which introduces warm currents and moisture
to the North Atlantic – resulting in increased snow fall and
formation of ice in Greenland, Laurentia and Fennoscandia.
The last million years…
Carbon dioxide
and methane
over last
500,000 years
Climate swings
between ice ages
and warm
inter-glacial periods
over last million
years.
CO2 between 180
and 300 parts per
million.
The last 10,000 years – the Holocene
Peak
Holocene
temp.
Peak Holocene: over last 10,000 years up 1900AD
Holocene: after the
last ice age, relatively
stable temperatures
(+/–0.5C) and sealevels over last 10,000
years – the period of
human civilisation
Today temperature rises above the Holocene maximum
CO2 level today is 393ppm but “thermal
inertia” (delay as ocean mass warm)
means temperature will increase further.
Temperatures have risen ~0.83C since
1900 and are now ~0.6C over peak
Holocene.
2010
Peak Holocene: over last 10,000 years up 1900AD
Global average temperature now ~0.6C above peak Holocene
2 degrees – goodbye to Greenland ice sheet…
When climate system
reaches equilibrium,
present level of CO2 will
produce >2C of warming
with feedbacks…
+2C
Peak Holocene: over last 10,000 years up 1900AD
Global average temperature now ~0.6C above peak Holocene
2C of warming: consequence of current level of greenhouse gases
… which is sufficient for large
parts of Greenland and West
Antarctic ice sheets to be lost,
leading to at least a 6-7 metre
sea-level rise over time
“Goals to limit human-made
warming to 2°C.. are not sufficient –
they are prescriptions for disaster”
— Dr James Hansen
+2C
Peak Holocene: over last 10,000 years up 1900AD
Global average temperature now ~0.6C above peak Holocene
2C of warming: consequence of current level of greenhouse gases
4 degrees – goodbye, goodbye …
Best present emission reduction
commitments by all governments
(if implemented) will still lead to
4 degrees of warming by 2100…
+4C
Peak Holocene: over last 10,000 years up 1900AD
Global average temperature now ~0.6C above peak Holocene
2C of warming: consequence of current level of greenhouse gases
4C of warming
…and likely loss overtime
of all ice sheets. No ice
sheets on planet = 70
metre sea-level rise over
time…
… amongst many devastating impacts.
Read more about 4 degrees hotter at
http://www.climateactioncentre.org/resources
+4C
Peak Holocene: over last 10,000 years up 1900AD
Global average temperature now ~0.6C above peak Holocene
2C of warming: consequence of current level of greenhouse gases
4C of warming
It’s up to you….