Lecture 2
觀測與推估 – IPCC AR4
Assessment Report (2007)
http://www.ipcc.ch/
Human and Natural Drivers of Climate
Change
1.
Global atmospheric concentrations of carbon dioxide,
methane and nitrous oxide have increased markedly as a
result of human activities since 1750 and now far exceed preindustrial values determined from ice cores spanning many
thousands of years. (溫室氣體含量）
2.
The understanding of anthropogenic warming and cooling
influences on climate has improved since the Third
Assessment Report (TAR 2001), leading to very high
confidence that the globally averaged net effect of human
activities since 1750 has been one of warming, with a radiative
forcing of +1.6 [+0.6 ~ +2.4] Watt m-2. （輻射作用）
(Radiative Forcing)
CO2: 280 ppm (pre-industrial value)
to 379 ppm (2005), exceeds the
natural range (180 to 300 ppm)
over the last 650,000 years.
Level Of
Scientific
Understanding
Direct Observations of Recent
Climate Change
1. Warming of our climate system is unequivocal, as is now
evident from observations of increases in global average
air and ocean temperatures, widespread melting of snow
and ice, and rising global mean sea level.
• Updated 100-year linear trend (1906–2005) of 0.74°C is larger
than the corresponding trend for 1901-2000 given in the TAR of
0.6°C.
• Balloon-borne and satellite measurements of lower- and midtropospheric temperature show warming rates that are similar to
those of the surface temperature record.
• average atmospheric water vapour content has increased since at
least the 1980s over land and ocean as well as in the upper
troposphere.
relative to 1961-1990
Not a good
news at all
8
Warming is
becoming
faster !
Linear trend of water
vapor content over
oceans is ~ 1.2% per
decade
9
The overall trend
of precipitation is
uncertain.
10
Spatial dist. of drought potential (1900-2002)
FAQ 3.2, Fig
11
Future Projection
Assessed Likelihood
• Virtually certain > 99% 幾乎確定
• Extremely likely > 95% 極端可能
• Very likely > 90% 非常可能
• Likely > 66% 可能
• More likely than not > 50% 比較可能
• Unlikely < 33% 不可能
• Very unlikely < 10% 非常不可能
• Extremely unlikely < 5% 極端不可能
Understanding and Attributing Climate
Change
1. Most of the observed increase in globally
averaged temperatures since the mid-20th
century is very likely due to the observed
increase in anthropogenic greenhouse gas
concentrations.
2. Discernible human influences now extend to
other aspects of climate, including ocean
warming, continental average temperatures,
temperature extremes and wind patterns
Projections of Future Changes
1.
A major advance of AR4 compared with the TAR is the large
number of simulations available from a broader range of
models.
2.
For the next two decades a warming of about 0.2°C per
decade is projected for a range of SRES emission scenarios.
Even if the concentrations of all greenhouse gases and
aerosols had been kept constant at year 2000 levels, a further
warming of about 0.1°C per decade would be expected.
3.
Continued greenhouse gas emissions at or above current rates
would cause further warming and induce many changes in
the global climate system during the 21st century that would
very likely be larger than those observed during the 20th
century.
17
18
A1.
The A1 storyline and scenario family describes a
future world of very rapid economic growth,
global population that peaks in mid-century and
declines thereafter, and the rapid introduction of
new and more efficient technologies. Major
underlying themes are convergence among
regions, capacity building and increased cultural
and social interactions, with a substantial
reduction in regional differences in per capita
income.
19
• A1
The A1 scenario family develops into three
groups that describe alternative directions of
technological change in the energy system.
The three A1 groups are distinguished by
their technological emphasis: fossil intensive
(A1FI), non-fossil energy sources (A1T), or a
balance across all sources (A1B) (where
balanced is defined as not relying too heavily
on one particular energy source, on the
assumption that similar improvement rates
apply to all energy supply and end use
technologies).
20
• A2.
The A2 storyline and scenario family describes a
very heterogeneous world. The underlying theme
is self-reliance and reservation of local identities.
Fertility patterns across regions converge very
slowly, which results in continuously increasing
population.
Economic development is primarily regionally
oriented and per capita economic growth and
technological change more fragmented and
slower than other storylines.
21
• B1.
The B1 storyline and scenario family describes a
convergent world with the same global
population, that peaks in mid-century and
declines thereafter, as in the A1 storyline, but
with rapid change in economic structures
toward a service and information economy, with
reductions in material intensity and the
introduction of clean and resource-efficient
technologies. The emphasis is on global solutions
to economic, social and environmental
sustainability, including improved equity, but
without additional climate initiatives
22
• B2.
The B2 storyline and scenario family describes
a world in which the emphasis is on local
solutions to economic, social and environmental
sustainability. It is a world with continuously
increasing global population, at a rate lower
than A2, intermediate levels of economic
development, and less rapid and more diverse
technological change than in the B1 and A1
storylines. While the scenario is also oriented
towards environmental protection and social
equity, it focuses on local and regional levels.
23
Scenarios
25
6.4
4.0
1.8
1.1
Future Tsfc changes (2090-2099, 2020-2029 vs. 1980-1999)
Future rainfall changes (2090-2099, vs. 1980-1999)
Consistency between models is not as good as Tsfc.
未來氣候變遷推估的科學信賴度
• 全球優於區域
• 全球大部分地區平均氣溫明顯上升
• 海水溫度明顯上升，海面明顯上升
• 雨量變化不確定性高，尤其是小區域（e.g.，台灣）
• 劇烈天氣與極端氣候發生頻率的變化，不確定性高
• 各項推估都有一定程度的 不確定性 (from various
sources)
認知與想法
IPCC AR4：
•
IPCC報告是根據數百（？）篇論文，整理出來的結果。
• 資料不完美，但或許是有史以來，最完整的資料。
• 模式仍有許多缺點，但是有史以來的最佳模式。
氣候變遷科學的本質：
• Projection, not prediction  Scenario Approach and Risk
Assessment (probability) (不精確科學）
• Small signal/noise ratio
• Forcing problem：
如果forcing夠大（如，> 560ppmv)  large signal/noise ratio?
 more reliable projection?
認知與想法
趨勢：
•
可預見的未來，沒有明顯跡象顯示溫室氣體排放會
顯著減緩
•
如果沒有顯著的全球性冷卻機制抗衡，暖化趨勢可
能性高
•
暖化地球的天氣與氣候 - 完全陌生的秘境
•
全面性影響？無任何尺度現象可以避免？
•
研究：From Cloud to Global Scale as an Integrated
System
問題：
• 不確定性高：尺度越小，不確定性越高
 如何將大尺度變遷信息降到台灣（甚至更小）尺度？
• 如何面對？
1.不確定性高，wait for mature technology and
definite result?
2.利用目前最佳資訊，採取風險評估策略，「反覆」
（調整）評估天氣與氣候的可能變遷？
策略：End-to-End Approach
歷史氣候變遷研究
…
動
態
調
整
機
制
…
未來氣候變遷研究
…
氣候變遷推估
衝擊研究與風險評估
政策規劃
成功的先決條件：1.紮實的基礎研究， 2.豐富的資料，3.良好的
工具，4. 良好的互動，5.足夠的時間與資源
以荷蘭為師？
~ End ~
• Average Arctic temperatures increased at almost twice the global average
rate in the past 100 years. Satellite data since 1978 show that annual average
Arctic sea ice extent has shrunk by 2.7 [2.1 to 3.3]% per decade, with larger
decreases in summer of 7.4 [5.0 to 9.8]% per decade.
• Significantly increased precipitation: eastern parts of North and South
America, northern Europe and northern and central Asia.
• Drying: Sahel, the Mediterranean, southern Africa and parts of southern
Asia.
• Long-term trends have not been observed for the other large regions
assessed.
• More intense and longer droughts have been observed over wider areas since
the 1970s, particularly in the tropics and subtropics.
• The frequency of heavy precipitation events has increased over most land
areas, consistent with warming and observed increases of atmospheric water
vapour.
• Widespread changes in extreme temperatures have been observed over the
last 50 years. Cold days, cold nights and frost have become less frequent,
while hot days, hot nights, and heat waves have become more frequent.
• There is observational evidence for an increase of intense
tropical cyclone activity in the North Atlantic since about
1970, correlated with increases of tropical sea surface
temperatures.
• There are also suggestions of increased intense tropical
cyclone activity in some other regions where concerns
over data quality are greater.
• Multi-decadal variability and the quality of the tropical
cyclone records prior to routine satellite observations in
about 1970 complicate the detection of long-term trends
in tropical cyclone activity.
• There is no clear trend in the annual numbers of tropical
cyclones.
2. Some aspects of climate have not been observed to
change.
• Updated observations reveal that DTR has not changed from 1979
to 2004 as both day- and night-time temperature have risen at about
the same rate. The trends are highly variable from one region to
another.
• Antarctic sea ice extent continues to show inter-annual variability
and localized changes but no statistically significant average trends,
consistent with the lack of warming reflected in atmospheric
temperatures averaged across the region.
• There is insufficient evidence to determine whether trends exist in
the meridional overturning circulation of the global ocean or in
small scale phenomena such as tornadoes, hail, lightning and duststorms.
A PALEOCLIMATIC PERSPECTIVE
• Paleoclimate
information
supports
the
interpretation that the warmth of the last half
century is unusual in at least the previous 1300
years. The last time the polar regions were
significantly warmer than present for an extended
period (about 125,000 years ago), reductions in
polar ice volume led to 4 to 6 metres of sea level
rise.
• The observed widespread warming of the atmosphere and
ocean, together with ice mass loss, support the conclusion that it
is extremely unlikely that global climate change of the past fifty
years can be explained without external forcing, and very likely
that it is not due to known natural causes alone.
• It is likely that there has been significant anthropogenic
warming over the past 50 years averaged over each continent
except Antarctica.
• Difficulties remain in reliably simulating and attributing
observed temperature changes at smaller scales. On these scales,
natural climate variability is relatively larger making it harder
to distinguish changes expected due to external forcings.
• Temperatures of the most extreme hot nights, cold nights and
cold days are likely to have increased due to anthropogenic
forcing. It is more likely than not that anthropogenic forcing has
increased the risk of heat waves.
• Warming is expected to be greatest over land and at most high
northern latitudes, and least over the Southern Ocean and parts
of the North Atlantic ocean.
• Snow cover is projected to contract. Sea ice is projected to
shrink in both the Arctic and Antarctic under all SRES
scenarios.
• It is very likely that hot extremes, heat waves, and heavy
precipitation events will continue to become more frequent.
• Based on a range of models, it is likely that future tropical
cyclones (typhoons and hurricanes) will become more intense,
with larger peak wind speeds and more heavy precipitation
associated with ongoing increases of tropical SSTs.
• Increases in the amount of precipitation are very likely in highlatitudes, while decreases are likely in most subtropical land
regions, continuing observed patterns in recent trends.