3. What climate changes are likely?
In terms of key environmental
parameters, the Earth system has recently
moved well outside the range of natural
variability exhibited over at least the last half
million years. The nature of changes now
occurring simultaneously in the Earth
System, their magnitude and rates of change
are unprecedented and unsustainable.
PAUL CRUTZEN (NOBEL LAUREATE) AND WILL STEFFEN
(INTERNATIONAL GEOSPHERE-BIOSPHERE
PROGRAMME, EXECUTIVE DIRECTOR), 2003
4. In the following chapter we will look at the
magnitude and rate of climate
change, including sea-level rise and changes
in extreme events, that are likely to result
from human-induced emissions of greenhouse
gases, and at what the effects might be on
nature and society.
5. IPCC has tried in successive reports to state
what it was confident about, and what was
more or less likely or possible, but still rather
uncertain. The statement from the American
Geophysical Union - the professional
association of American geophysical scientists
does the same……
7. Surface warming
The IPCC’s 2001 report projects global average surface
temperature increases ranging from 1.4 to 5.8°C by 2100.
8. The corresponding range from the 2007 IPCC report is 1.1 to
6.4°C.
This latest projected rate of warming is roughly two to 10
times that observed during the twentieth century, which
was about 0.6°C.
The rate is much faster than the average warming at the
end of the last glaciations.
The greater warming at the high end of the range,
compared to that in the IS92 range is due to both greater
carbon dioxide emissions in the high emissions scenarios
and less sulfur emissions.
9.
10. Regional warming
The least warming is expected over the Southern Ocean
due to its large capacity to transport surface heat into the
deep ocean, and possibly in the North Atlantic
region, depending on the behavior of the ocean circulation.
High northern latitudes may warm at several times the rate
of the global average.
Warming may be greater in the eastern tropical Pacific
than in the west.
After stabilization of greenhouse gas concentrations in the
atmosphere, warming will continue for centuries.
11. Precipitation and Evaporation
Global average precipitation and evaporation are
projected by climate models to increase by about 1 to
9% by 2100.
Decreases in annual average precipitation in the
subtropical and mid-latitudes are up to 20% in the
climate models by 2100.
Total water content of the atmosphere will increase at
around 7% for each °C rise in global surface
temperature.
12. Xuebin Zhang and colleagues in a study to detect
human influence on twentieth century that
precipitation has changed faster than the climate
models have predicted.
13. Extreme Events
According to the IPCC 2007 report, it is likely that changes
in some extreme events were observed during the
twentieth century.
Higher maximum temperatures and more hot days over
nearly all land areas.
Higher minimum temperatures, fewer cold days and
frost days over nearly all land areas.
Reduced diurnal temperature range over most land
areas.
14. Intense precipitation events, (frequency or proportion
of total rainfall).
Increased risk of drought in mid-latitude continental
areas.
Increase in tropical cyclone peak wind intensities and
rainfall, with lower central pressures.
Extreme extra-tropical storms: increased frequency
and pole wards shift.
Coastal storm surges and flooding more severe (due to
both higher mean sea level and more intense storms).
15. Sea-Level Rise
Sea-level rise is obviously important, given that a rapidly
increasing number of people live in lowlying coastal
areas and there is massive investment in
infrastructure, including cities, ports, refineries, power
stations and tourist resorts.
Projections of global sea-level rise by the IPCC in 2001
ranged from 9 to 88 cm by 2100, but in the 2007 report
the upfront ‘model-based’ estimate was 18 to 59 cm.
Melt water from mountain glaciers and a contribution
due to increased ice flow from Greenland and
Antarctica.
16.
17. If greenhouse gas concentrations were stabilized, the
2007 IPCC report notes that sea-level rise would
continue for hundreds of years, due to the slow but
continuing warming of the deep oceans and the
contraction of the Greenland ice sheet.
The Greenland Ice Sheet is at a generally lower latitude
than Antarctica and has widespread marginal surface
melting in summer. The area of surface melting has
rapidly increased in recent years. (since 2002)
18. Abrupt or Irreversible Changes
Thermo-Haline Circulation,
The rapid disappearance of Arctic sea ice,
Rapid loss or disappearance of mountain glaciers or ice
caps,
Increased melting or collapse of the Greenland or
West Antarctic ice sheets,
Large-scale vegetation change such as desertification,
or vegetation and soils turning into sources rather than
sinks of carbon,
19. Scenarios in a nutshell/Summary
In summary, the full range of IPCC emissions scenarios
would lead to a wide range of global warming (1.1 to
6.4°C) and sea-level rise (18 to 59 cm according to
IPCC 2007, but more likely 1 meter and up to several
meters) by 2100. About half the range in global average
warming is due to the range of emissions scenarios and
half to uncertainties in the science, mainly in the
climate sensitivity.
