global climate change: what do we know & what don’t we know?* klaus wolter university of...
TRANSCRIPT
Global Climate Change: What do we know & What don’t we know?*
Klaus Wolter
University of Colorado at Boulder, [email protected]
Kudos to Susan Solomon (most unmarked slides)
(Co-Chair of WG 1, IPCC 4; a.k.a. “The Horse’s Mouth”)
• Background on IPCC & Global Change modeling
• Observed climate changes & how well they are modeled
• Projections through the 21st century
• Closing thoughts
* With two nods to our former Secretary of Defense (also: “you have to analyze climate change with the data you have got…”)
Structure of the IPCC
Socio-economics, policy options, discount rates, emission scenarios,…..
Flowering dates, corals, coastal zone erosion,….
WG1 - Climate Change:The Physical
Science Basis
WG2 - Climate Change: Impacts and Adaptation
WG3: Mitigation
Three different working groups with quite distinct scientific purviews and required expertise. IPCC assesses research but it doesn’t do research. WG1 report is at ipcc-wg1.ucar.edu.
The IPCC Sequence
IPCC (1990) Broad overview of climate change science, discussion of uncertainties and evidence for warming.
IPCC (1995) “The balance of evidence suggests a discernible human influence on global climate.”
IPCC (2001) “Most of the warming of the past 50 years is likely (>66%) to be attributable to human activities.”
IPCC (2007) “Warming is unequivocal, and most of the warming of the past 50 years is very likely (90%) due to increases in greenhouse gases.”
Intergovernmental Panel on Climate Change, UN-approved since 1988, 75% of 2007 WG-1 authors did not work on last assessment (2001,Third Assessment Report).
Latest info on GHG
There is no debate whether greenhouse gases are rising - the evidence is clear-cut that their (carbon dioxide, methane+) levels have been rising to (& at) unprecedented levels (rates) longer than homo sapiens has existed (at least 600K, actually), and as best as I can tell there is little debate as to whether this increase is human-caused.
IPCC, 2007: SPM 2
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Last Ice Age
Humans are ‘forcing’ the earth system in a new way. CO2 increases due to fossil fuel burning are the dominant cause of global warming. CO2 has not been this high in more than half a million years.
Last interglacial
Ice ages are not random. They are 'forced' (by earth’s orbital clock…. changes in the sunlight received).
350
300
250
200
Carb
on
Dio
xid
e A
mou
nt
(pp
mv)
600 500 400 300 200 100 0
Thousands of Years Before Present
[Adapted from Figure 6.3, ©IPCC 2007: WG1-AR4]
Better and longer satellite data about the Sun
Improved assessment: a) no significant observed trend in solar irradiance since 1978
using high quality inter-calibrated data; b) spectral information c) solar magnetic flux model rather than proxy data; d) re-evaluation of variations in Sun-like stars.
Solar irradiance forcing much smaller than GHG, and then TAR estimates.
Observations reveal the presence and provide quantitative aspects. Aerosol transport-forcing models better tested and constrained. Much improved estimate of the Aerosol Direct Radiative Forcing.
January to March, 2001
New information about aerosols, and major modelling improvements
Human and Natural Drivers of Climate Change
1.6 W m-2 warms like 1.6 xmas tree lights over every m2 on Earth.
Carbon dioxide is causing the bulk of the forcing, and it lives a long time in our atmosphere so every year of emission means commitments to climate change for future generations.
IPCC, 2007: SPM 2
Figure 10.1
IPCC, 2007: 10.1
Figure 3.1
IPCC, 2007: 3.1 - Observed temperature changes since 1850 (different QC/averages)
Observed climate changes & how well they are modeled
Correlativity of U.S. climate stations (DJF temps 1979-03)
Correlativity tends to be highest in the winter. Iowa winter temperatures could be monitored by just a few (one?) stations, while Colorado has many more ‘local flavors’. (Wolter and Allured; http://www.cdc.noaa.gov/people/klaus.wolter/ClimateDivisions)
Figure 3.2
IPCC, 2007: 3.2 - land data
IPCC, 2007: 3.9 - °C per century on left/per decade on right (and below); grey = insufficient data
IPCC, 2007: FAQ 3.1 - MSU-based trends for last 25 years (better match than in TAR)
Figure 3.10
IPCC, 2007: 3.10 - 18 years of data (≥2 months per season) requred; sensitive to end points!
Figure 3.12
IPCC, 2007: 3.12 - a lot more “enthusiasm” about wetting trend in/after TAR!
Figure 3.13
IPCC, 2007: 3.13 - note contrast between two periods in Western U.S. and Sahel!
Figure 4.1
IPCC, 2007: 4.1 - Components of cryosphere & their time scales
Figure 4.2
IPCC, 2007: 4.2 (March-August dropping; September-February NOT - WHY?)
Figure 4.8
IPCC, 2007: 4.8 - NH dropping (spring& summer!); SH not - WHY?
Figure 4.15
IPCC, 2007: 4.15 - specific vs. total glacier mass balance (regional strength of climate change vs. contribution to sea level rise)
Figure 4.23
IPCC, 2007: 4.23 - Summary slide
Attribution• Asks whether observed changes
are consistent with expected responses to forcings inconsistent with alternative
explanations
• Most of the observed increase in globally averaged temperatures since the 1970s is very likely (>90%) due to the observed increase in anthropogenic greenhouse gas concentrations
TS-23
Anthro+ Nat forcing
Understanding and Attributing Climate Change
Anthropogenic effect on warming
averaged over each continent except
Antarctica is likely [IPCC, 2007]
Observed
Expected for all forcings
Natural forcing only
Understanding and Attributing Climate Change
Anthropogenic effect on warming
averaged over each continent except
Antarctica is likely [IPCC, 2007]
Observed
Expected for all forcings
Natural forcing only
Attribution studies
• Separate time-space patterns of response.
• Solar response has very different behavior to GHG, especially with altitude. The upper atmosphere would be expected to be much warmer than it is if solar irradiance were the cause of current surface climate change.
Solar
“All” forcings
Figure 3.27
IPCC, 2007: 3.27 - SLP/Tsfc/Precip vs. SOI - step change around ‘76?!
Figure 3.33
IPCC, 2007: 3.33 - AMO: main driver for Atlantic hurricane trends?!
IPCC, 2007: 3.38 (10th percentile for 1901-50 (black), 51-78 (blue), and 79-03 (red)
Figure 3.39
IPCC, 2007: 3.39 - contribution from very wet days (95th percentile) to annual precip
Figure 3.40
IPCC, 2007: 3.40 - Accumulated Cyclone Energy (ACE); still much debate on how much of the recent increase in North Atlantic is related to natural climate variability (AMO) vs. anthropogenic; there are also quite a few (poorly resolved) inhomogeneities in record (Landsea, 2007; pers. comm.)
Calculus of extremes
Standard deviation
1 in 40 yr high range
The distribution of weather events around the climatic average often follows a ‘bell-shaped’ curve.
Climate change can involve change in the average, or the spread around the average (standard deviation), or both.
A shift in temperature distribution has much larger relative effect in the tails than near the mean. For instance, huge JJA’03 anomaly in Europe (>5 sigma) is more consistent with higher sigma than with higher mean.
A shift of 1 standard deviation makes a 1 in 40 yr event into a 1 in 6 yr event
Projections through the 21st century
Figure 10.2
IPCC, 2007: 10.2
Committed Warming is Coming
• For the next two decades a warming of about 0.2°C per decade is projected for a range of emission scenarios.
• Even if the concentrations of all greenhouse gases and aerosols were to be kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.
The Longer TermWarming will increase if GHGs increase. If GHGs were kept fixed at current levels, a committed 0.6°C of further warming would be expected by 2100. Higher emissions translate into more warming.
1.8oC = 3.2oF
2.8oC = 5.0oF
3.4oC = 6.1oF850
600
4000.6oC = 1.0oF
Projections of Future Changes in Climate: Probabilistic Information for the First Time
Changes over next few decades already ‘locked in’ (to the extent that the models can provide the answer), big differences by end of century
Seasonal moisture changes as projected for DJF and JJA
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Wetter in winter & drier in the summer, if you believe the model average…
Bottomline on regional climates (&trends)
VAR = GHG + Decadal + ENSO + Regional + Local + Noise
(not everything is greenhouse-related, nor will it ever be & don’t underestimate the “noise”=our (in-) ability to measure correctly)
We do NOT fully understand all of the above components of the climate system, leaving room for surprises!
This is my opinion, not the IPCC’s!
Figure 10.14
IPCC, 2007: 10.14 - Sea ice projections
Figure 10.16
IPCC, 2007: 10.16 - are we going to get more/stronger El Niños???
Figure 10.18
Figure 10.32
IPCC, 2007: 10.32 - sea leve change for end of 21st century relative to expected global average change
Figure 10.38
Figure 11.12
IPCC, 2007: 11.12 - problem with regional ‘down-scaled’ scenarios: models that are good in present are not guaranteed to stay good; high fidelity in temp reconstructions/ projections does NOT translate into good precip reconstructions/projections
Box 11.1, Figure 2
Some Pressing Needs for a WG1 AR5…. (Susan Solomon)
• Forcing: How well do we understand past history of emissions and forcing? Future? Aerosol effects on precip? Role of soot? Land use? Stabilization of GHG (if governments so decide) is linked to understanding of forcing/feedback relationships (esp. carbon).
• Beyond global warming: The AR5 will likely advance the understanding of hurricanes, drought, heat waves, other extremes, precipitation patterns, ocean circulation, and other ‘earth system’ variables, for observations, attribution, and projections. Much more regional information will likely be sought, and as in the AR4, this should follow on the basis of physics (not catalogues). Central to understanding the adaptation/mitigation challenges.
• Near-term: Already committed to more warming (next few decades), with choices about emissions affecting the longer term more and more…commitments to SLR? Drought? Heat waves? Hurricanes?
• Long term: SLR changes the face of the planet. The next assessment will likely advance understanding of ice sheets and SLR.