Present from 350: Monica, Neal, Amelia Rose, Stuart, Milan
Global Warming "Futures"W. Richard Peltier
Professor of Physics - Atmospheric Physics and Geophysics
Department of Physics
University of Toronto
'Bambi meets Godzilla'
* CC not just moving the goalposts, but could be a game-changer
* Risks undermining other human efforts
*
https://www.youtube.com/watch?v=n-wUdetAAlYThe active sun and the amplification of its power by the greenhouse effect
Climate change not well presented in the popular press
* "Leaves the public with the impression that the debate is equally joined on all sides"
* Confidence well above the 95% level, verging on the 99% level
Forthcoming IPCC AR5
* Coming out next month
Three main radially active gases: CO2, CH4, N2O
* Ongoing rise triggered by coal-burning during Industrial Revolution
* Planet radiates longwave radiation into space - Some emitted energy captured by greenhouse gases, some emitted back to the Earth's surface
* This is at the heart of the enhanced greenhouse effect
'Hockey stick' graph from the IPCC AR3
*
https://upload.wikimedia.org/wikipedia/commons/e/ed/Hockey_stick_chart_ipcc_large.jpg* Michael Mann initially 'widely pilloried' for this chart
* US Senate demanded that he "provide his software"
What is the source of this temperature data?
* Reconstruction based on proxy data: width of tree rings, sedimentation in deep lakes near the tropics and poles, forams, corals
* Transfer function exists between the measure in each proxy and the temperature
Over the last 150 years, the temperature has risen to well above any temperature observed for at least the last 1000 years
How can scientists be confident in this temperature and CO2 record?
* There is a very strong correlation between mean global temperature and CO2 concentration
Jump in CO2 caused by fossil fuel burning and land use change (deforestation, land-clearing for agriculture)
Around 20,000 years ago, there were massive concentrations of land ice around the poles
* Extended from coast of arctic ocean almost down to the present US-Canada border
* 4km deep
* Last glacial maximum
* During this time, GHGs were much lower in concentration than subsequently
* Deglaciation was over about 10,000 years ago - beginning of the Holocene
During the last 150 years, there has been a spike in CO2 and the other trace gases
Data from ice cores
* CO2, CH4, and N2O, temperature
* Vostok ice core:
https://en.wikipedia.org/wiki/Ice_core#Vostok* Gas measurements from centimetre thick core segments made in France, after being melted in vacuum
* Snow eventually gets so compacted in the ice sheet that it is no longer in contact with the atmosphere
* We now have cores that go back over 800,000 years
Every 100,000 years, there is a characteristic shape to the changes in concentration of GHGs
* Continuous glaciation and deglaciation in the northern hemisphere
* During glaciation, CO2 has a positive feedback on cooling, accelerating the process
* During times of warming, CO2 has a positive feedback relationship with warming
Ice core measurements match up exactly with more recent instrumented measurement
* This means our 800,000 year record is equivalent to a person with modern equipment sitting at Vostok and collecting data across this whole span
Why do the measurements from this site reflect global concentrations?
* GHGs are well mixed in the atmosphere
This was "a phenomenal discovery in Earth science"
* "This Earth has been remembering what has been happening to it"
'''Observations of Warming in Time and Space and at the Poles'''
The GRACE satellites
* Gravity Recovery and Climate Experiment mission:
https://en.wikipedia.org/wiki/Gravity_Recovery_and_Climate_ExperimentSince industrialization, the mean surface temperature has increased by about 0.8˚C
* There was a pause between about 1940 and 1970
* Why?
* "Very well understood consequence of competing interactions in the climate system"
* Main one: atmospheric aerosols:
https://en.wikipedia.org/wiki/Atmospheric_particulate_matter* Mostly have a cooling effect, because they reflect shortwave radiation directly back into space
ENSO events also have an impact:
https://en.wikipedia.org/wiki/El_Ni%C3%B1o%E2%80%93Southern_Oscillation* Result of air-sea interaction
Warming of the surface has varied between regions
* Clear on decadal scales, compared to the 1940-1970 period
* More warming over land than over oceans, at an increasing rate
* "Very clearly understood - completely unarguable"
* Heat capacity of land is less than that of oceans, so there is more warming for any particular energy input
* Land and ocean in high northern latitudes - near the north pole - warming much more rapidly than the rest of the Earth's surface
* One cause: albedo feedback
* White ice reflects shortwave radiation directly back into space
Continental Ice-Sheets and Glaciers in the Modern Climate System: Polar "Canaries"
* Warming in northern Canada 2.5X the warming on the planet's surface as a whole - "polar amplification"
* Antarctica contains enough ice to raise global sea level by about 70 m - 230 feet
* Greenland could raise global sea levels by 7 - 7.5m
There has been great interest in monitoring changes to land ice
* GRACE satellites - almost polar orbit, over 100km between them
* Distance between measured via microwave link
* Accurate to the width of a human hair, made interferometrically
* Future project will use lasers and increase accuracy by an order of magnitude
Data from GRACE
* Over the entire Canadian landmass, there is an increasing amount of mass below the satellite - not a result of ice sheets
* Consequence of icostatic rebound:
https://en.wikipedia.org/wiki/Post-glacial_rebound* Land that was pushed down by icesheets during last ice age is slowly bouncing back
* There are also changes in surface hydrology - water trapped in soil layers - one consequence of ongoing climate change
* Global Land Data Simulation Scheme
We can isolate the data on changing ice sheets from the changes from isostatic rebound
We can translate gravity measures of ice loss into measures of global sea level rise
* Greenland - about 0.6mm per year
* Antarctica - data must also be corrected for ancient ice age influence - 2 regions known to be losing ice (including Amundsen sea) - delivers 0.3-0.4mm / year of global sea level rise
Climate models are mathematical structures that comprehensively include the atmosphere, oceans, sea ice, and land biosphere
* Typical models now very comprehensive
* Based on large set of partial differential equations, solved on a very fine grid
* Studying evolution of the mean properties of the system over long timescales
Many people in the climate denial industry raise issues about models
* Recent Senate hearing in Ottawa - 4 of the more prominent climate deniers invited to participate by the government
* "They never studied second-year physics"
* Argued that water vapour is the most important GHG
* "At the heart of a lot of the ignorance that populates the discussion in the climate change debate"
* You need to distinguish between prime movers and feedbacks
* Clapeyron-Clausius relation:
https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation* Warmer air holds more water
Projecting future climate change requires making an assumption about what future emissions will be
* This is a public policy issue
* The IPCC SRES scenarios:
https://en.wikipedia.org/wiki/Special_Report_on_Emissions_Scenarios* A2 scenario usually referred to as business-as-usual
* A1B, modest policy intervention to try to reduce the amount of warming (not enough to stabilize at 350ppm)
* B1 is a scenario that should keep us below 2˚C
Two of the most important messages
* 16 different national models run out to 2300 for the IPCC AR4
* Based on different scenarios between 2000 and 2100
* Not much difference until beyond mid-century, between different emission pathways
* This has a big impact on the political process - politicians not concerned about conditions in 30 years
* "there is no incentive here for rapid action"
* After 2070 "the differences become very significant"
2˚C probably isn't the 'must not rise above' temperature, but speaker doesn't know exactly where it is
* Uncertainty about feedbacks
Attribution of the enhanced greenhouse effect
* Comparing models that eliminate the rise of GHGs from others where historical data is used
* Observed temperatures follow the GHG model, not the one that ignores them
* Clear starting between 1960s and 70s - signal rose above noise
*
https://www.sindark.com/wp/wp-content/uploads/2009/10/ccattribution.PNGDownscaling for Ontario:
* Projections for 2050 based on A2 and A1B
* By end-century, mean temperature up by about 5˚C over Ontario and the Great Lakes basin
Questions:
1) What impact will this have on methane, and what will the impact be?
Models don't do a good job of describing the extent of permafrost melting that is happening now in Canada and Russia
* A lot of work is being done on this in the modelling community
* New satellite program will try to measure methane concentrations from space
2) What other impacts can be expected?
Most severe impacts likely to be the frequency of extreme events
* 100-year events has now shrunk to about 50 for droughts and severe precipitation events
* As air warms, it holds more water vapour - not returned to the surface in a smooth way
* Events become progressively more severe as the air holds more water vapour
3) Do you feel like Cassandra? You can predict the future, but not enough people are listening. How do we close this disconnect?
"My friend Jim Hansen will chain himself to a fence outside the White House"
* This is a reasonable response to what's happening
"I give talks in church basements"
"The population must become sufficiently well-educated to understand the truth of it all"
* Must be willing to look at the data and think about what they mean
4) What is likely to happen in areas of the world with less moderate climates than Ontario?
In terms of precipitation events, all of the models agree that the wet get wetter and the dry get drier
* Where there are drought conditions now, the droughts will get more severe
* Places like Vancouver will get even wetter
* US Southwest has now been in drought conditions for about 20 years
5) Do the latest models provide more accurate predictions for sea ice loss than earlier models?
Speaker uses a model developed at the US centre for atmospheric research -
https://en.wikipedia.org/wiki/National_Center_for_Atmospheric_Research* Only model that came anywhere close to modelling recent arctic sea ice losses
* Includes description of melt ponds on the surface of the ice
As computers get more powerful, we can know more
The latest incarnation of the NCAR model predicts totally absent sea ice around 2030-40 at the October minimum
* No multi-year ice
* Earlier estimates of 2070-80 were "far too conservative"
6) Some people predict that it will be done in a few years. Responses?
Outlandish claims attract disproportionate attention
* But you pay the price if you turn out to be wrong
* "That's how science invigilates itself"
"Unwise to go way out on a limb"
Website worth looking at:
http://realclimate.org/7) In what ways can people advocate for change?
"We currently have a government in power in Ottawa that is absolutely outrageous"
* "We have to insist on being knowledgeable"