1. Has global warming stalled?
Air Temperatures

2. Air temperature data from 1970 to 2013
Air Temperatures

3. The truth is that the last decade of global air temperatures has been the hottest on record.
But it is also true that air temperatures for the last decade have plateaued.

4. Specific heats:
The amount of heat needed to raise 1 gram of air (at 1 atm pressure) 1° C = 0.24 calories
The amount of heat needed to raise 1 gram of water 1° C = 1 calorie
Latent heat of fusion:
The amount of heat needed to melt 1 gram of ice to water at 0° C= 80 calories

5. The ocean is roughly 400 times more massive than the atmosphere.
Therefore the amount of heat needed to raise the atmosphere only 1° C would heat the oceans only a fraction of a degree.
The amount of heat needed to melt glaciers and ice caps at 0° C is tremendous.
Therefore a huge amount of heat can be absorbed by the oceans and by melting glaciers without a noticeable increase in temperature.
Global heating by the greenhouse effect is much more than raising the temperature of the atmosphere.

6. More than 90% of global warming heat goes into warming the oceans, while less than 3% goes into increasing the surface air temperature.
Nuccitelli et al 2012 Total Heat Content

7. Is it really getting warmer??
Is recent temperature change outside the range of natural variation?
Why is it getting warmer?
What role might greenhouse gases play?
Is it going to keep getting warmer?
What are the possible dangers of warming?

8. Reconstructed global average T for past 150 years, relative to the 1961-1990 average

9. Reconstructed T for past 1000 years

10. Other evidence
for warming:
Retreat of glaciers
Here, ice cap on
Mt Kilamanjaro in 1978(top) and
1998 (bottom).

11. Global Warming Mountain glaciers are shrinking Sea Level is rising
CO2 in the atmosphere is increasing

12. Locations of Glaciers

15. Rising sea level
Sea level appears to be very slowly rising on a global average
Caused by two things
Thermal expansion of ocean water itself
Melting of land ice

16. Tide gauges for European cities

17. Average sea surface heights since 1993

18. Records of Climate Change
Instrumental (~200 yr at best)
Written descriptions(~1000 yr)
Tree Rings (~10,000 yr)
Ice Cores (~100,000 yr)
Coral Reefs (~100,000 yr)
Biogenic Ocean Sediments (to~100 My)
Sediment deposits (to ~1 billion y)

20. Is it getting warmer?....Yes
The latter half of the 20th century is significantly warmer than at any time in the past 1000 years
There is really NO scientific debate that temperatures have been increasing in the past 100 to 150 years
But is this outside the range of natural variation?

21. More detailed look at climate in the Cenozoic (last 65 my) from Oxygen Isotopes
Isotopes of an element have same number of protons.
Differ by number of neutrons
Chemically identical
Only processes that are mass dependent can separate isotopes

22. These are ‘stable’ isotopes, not radioactive

23. Stable Isotopes "Normal" Oxygen (light) 8 Protons, 8 Neutrons
16 = Total Mass 16O
“Rare" Oxygen (heavy)
8 Protons, 10 Neutrons
18 = Total Mass 18O
Measure Ratio: 18O/16O

24. Why ????
It turns out that the 18O/16O ratio of calcite that is produced by marine organisms is partly controlled by TEMPERATURE (as long as the 18O/16O of seawater stays the same…more later!)
If temperatures get warmer, the 18O/16O of calcite will decrease and vice versa…so we have a paleo-thermometer.

25. Foraminifera as Chemists
Calcium Carbonate - CaCO3
Oxygen isotope ratio of the CaCO3 is
related to
temperature
of seawater.

26. Coccolithophores a type of marine algae, also make CaCO3
More foraminifera, small marine animals

28. Record of Earth ‘average T’ for the past 65 million years
This record is composed on thousands of O isotope analyses from many locations
Record is from ‘benthic’ foraminifera – those living on the ocean floor
Primarily shows that the Earth has been slowly cooling since about 65 m.y. ago
The Cretaceous and early Cenozoic were much warmer than today – no ice caps in Antarctica or Greenland, as there are now

29. Ice Core Research Greenland • over 2 km of ice
• deepest ice is ~130,000 years old
2) Antarctica
• also about 2 km of ice
• deepest ice is >400,000 years old
3) Tropical mountains
• deepest ice is ~10,000 years old
3) In all areas 18O/16O of the snow (H2O) is highly correlated to temperature

30. Ice core sites

35. Estimate of T change for past 18000 years
Note that for some time periods, about 8000 to 4000 years ago and about 1000 years ago T might have been 1 degree C warmer than last 100 years

36. Is recent T change outside the range of natural variation
Is recent T change outside the range of natural variation? Maybe, maybe not
But the overall natural trend has been towards cooler T over the past 1000 years and even longer
The recent increase is coincident with a very un-natural rise in CO2 levels of the atmosphere that are the result of human activity
Are the two related?

37. The ice cores contain another very valuable type of information – the composition of the atmosphere. Air is trapped as bubbles in the ice as it is compressed from snow flakes to solid ice. These bubbles can be analyzed to see e.g. how much CO2 was in the air. So we have a record of the green house gas concentrations for the past 400,000 years.
snow
‘firn’
ice
trapped air

40. But are CO2 and T related?

43. Other trace gases also important:
N2 and O2 comprise > 99% of the atmosphere; neither absorbs significant radiation.
The primary gaseous absorbers in the atmosphere are, in order of importance
H20, water vapor
CO2,
O3 , ozone
Other trace gases also important:
CH4, methane
NO2 nitrous oxide
CFC’s
Greenhouse gases keep earth’s climate about 50C warmer than it would otherwise be.

46. Relative contribution to greenhouse forcing by individual gases (other than H20)

47. Relative sources of greenhouse gases

49. How can we estimate the effect of GHGs on climate?
Only way is to use computer models of the ocean/land/atmosphere system
Called ‘General circulation models’
As much as possible based on physics of atmosphere and measured parameters of its constituents
Include other ‘natural’ factors that might change climate: solar activity and volcanic activity are the main two

50. Results???
Nearly all models suggest that recent temperature change cannot be due to natural variation in climate
Only when GHG forcing is included in the models do they lead to the observed T change
Following are comparisons of models with only ‘natural’ forcing, only GHG and both, and observed T variation.

52. The future???
Models can also be used to project future climate change.
Below are results for many models, giving global average T, precipitation, and sea level.
These figure are from the Intergovernmental Panel on Climate Change report, “Climate change 2001; The Scientific Basis”
See for full report

53. Future trends in
GHG content of the atmosphere?
Here is an estimate of future oil use, but does this agree with Hubert’s curves?

54. Estimates of the future CO2 concentration in the atmosphere.

55. Estimates of global temperature change.

56. Estimates of global sea level rise.

57. Sea level controls

58. Plausible Impacts
Higher maximum temperatures and more hot days and heat waves over land areas (VL).
Higher minimum temperatures and fewer cold days, frost days and cold waves (VL).
More intense precipitation events over many areas (VL).
Increased summer drying over most mid-latitude continental interiors and associated risk of drought (L).
Intensified droughts and floods associated with El Nino events in many different regions (L).
Note: Judgmental estimates - VL = % chance; L = % chance that result is true.

59. Plausible Impacts for the U.S.
Reduced lake levels and outflows for the Great Lakes/St.Lawrence (MC).
Enhanced coastal erosion, flooding, loss of wetlands and increased storm surges especially off FL and much of the Atlantic coast (HC).
Vector-borne diseases may expand ranges in North America (MC).
Exacerbated air quality and heat stress morbidity and mortality may occur (MC).
Weather-related insured losses and public sector disaster relief payments in N.America have been increasing - potential for surprises (HC).
Note: Judgmental estimates - HC = %; MC = %.
Source: IPCC SPM, Third Assessment Report, Climate Change 2001: Impacts, Adaptation and Vulnerability, 2001.