May 14, 2013

Observations and Impacts

World Bank: Four Degree World

Extreme Events in the Period 2000–2012
(Adapted from Table 1, p 18)
[Unusual] weather events for which there is now substantial scientific evidence linking them to global warming with medium to high levels of confidence. (p 16)
Region (Year)Record-breaking EventImpact, costs
England and Wales (2000)Wettest autumn since records began in 1766
Several short-term rainfall records
~ £1.3 billion
Europe (2003)Hottest summer in at least 500 yearsDeath toll exceeding 70,000
England and Wales (2007)Wettest May to July 1766Major flooding
~£3 billion damage
Southern Europe (2007)Hottest summer in Greece since 1891Devastating wildfires
Eastern Mediterranean, Middle-East (2008)Driest winter since 1902Substantial damage to cereal production
Victoria, Australia (2009)Heat wave
Many station temperature records (32–154 years of data)
Worst bushfires on record
173 deaths
3,500 houses destroyed
Western Russia (2010)Hottest summer since 1500500 wildfires around Moscow
Crop failure of ~25%
Death toll ~55,000
~US$15B in economic losses
Western Europe (2011)Hottest and driest spring in France since 1880French grain harvest down by 12%
Texas, Oklahoma, New Mexico, Louisiana (2011)Record-breaking summer heat and drought since 1880Wildfires burning 3 million acres
(Preliminary impact of $6 to $8 billion)
Continental US (2012)Warmest July since 1895
Severe drought conditions
Abrupt increase in global food prices due to crop losses

Heat Waves and Extreme Temperatures

These events were … typically more than 3 standard deviations (sigma) warmer than the local mean temperature …
[Such] 3-sigma events would be expected to occur [by chance] only once in several hundreds of years.

The five hottest summers in Europe since 1500 all occurred after 2002, with 2003 and 2010 being exceptional outliers.
[During] the 2003 heat wave … daily excess mortality [reached] up to 2,200 in France. …
(p 13)

On August 28, [2012,] about 63% of the contiguous United States was affected by drought conditions … and the January to August period was the warmest ever recorded.
[Wildfires set] a new record for total burned area — exceeding 7.72 million acres.

In the 1960s, summertime extremes of more than three standard deviations warmer than the mean of the climate were practically absent, affecting less than 1% of the Earth’s surface. …
Now such extremely hot outliers typically cover about 10% of the land area.
(p 14)

Arctic Sea Ice Melt

Stefan Rahmstorf

Figure 3-5
Arctic Sea Ice Cover in September (the Summer Minimum Extent) in 1979 [the first year of satellite observation] and in 2005.
(NASA, May, 2007)
(Anthropogenic Climate Change: Revisiting the Facts, In E Zedillo, Global Warming: Looking Beyond Kyoto, Brookings Institution Press, pp 34–53, 2008)

World Meteorological Organization

Arctic sea ice extent reached its record lowest [annual minimum in the last 1,500 years on] 16 September [2012.]
This value broke the previous record low set on 18 September 2007 by 18 per cent [and] was 49 per cent … below the 1979–2000 average minimum.
The difference between the maximum Arctic sea-ice extent on 20 March and the lowest minimum extent on 16 September was 11.83 million km^2 — the largest seasonal sea-ice extent loss in the 34-year satellite record.

(WMO Annual Climate Statement Confirms 2012 as Among Top Ten Warmest Years, Press Release No 972, 2 May, 2013)

Would you like to know more?


The Rise of CO2 Concentrations and Emissions

Rising Global Mean Temperature

Increasing Ocean Heat Storage

Rising Sea Levels

Increasing Loss of Ice from Greenland and Antarctica

Ocean Acidification

Loss of Arctic Sea Ice

Drought and Aridity Trends

Agricultural Impacts

Possible Mechanism for Extreme Event Synchronization

Welfare Impacts


  • Turn Down the Heat, Potsdam Institute for Climate Impact Research and Climate Analytics, International Bank for Reconstruction and Development / The World Bank, November, 2012.


    The Rise of CO2 Concentrations and Emissions

    [Systematic] measurements of atmospheric CO2 emissions … show an increase from 316 ppm (parts per million) in March 1958 to 391 ppm in September 2012. …
    [Preindustrial] CO2 concentrations have been shown to have been in the range of 260 to 280 ppm [by ice-core measurements.]
    Geological and paleo-climatic evidence makes clear that the present atmospheric CO2 concentrations are higher than at any time in the last 15 million years.

    Figure 1
    Atmospheric CO2 concentrations at Mauna Loa Observatory.

    Since 1959, approximately 350 billion metric tons of carbon (or GtC)3 have been emitted through human activity, of which 55% has been taken up by the oceans and land, with the rest remaining in the atmosphere.
    (p 5)

    [Without intervention] global CO2 emissions [will rise to] 41 billion metric tons of CO2 per year [and total] greenhouse gases … to 56 GtCO2e [per year by 2020.]
    If current pledges are fully implemented, global total greenhouse gases emissions … are likely to be between 53 and 55 billion metric tons CO2e per year [by 2020.]

    Figure 2B
    [Total] greenhouse gases historic (solid lines) and projected (dashed lines) emissions.
    (Climate Action Tracker)

    Rising Global Mean Temperature

    Global mean warming is now approximately 0.8°C above preindustrial levels. …
    [The] observed warming cannot be explained by natural factors alone and thus can largely be attributed to anthropogenic influence.

    Figure 3
    Temperature data {corrected for short-term temperature variability (El Nino/Southern Oscillation, volcanic aerosols and solar variability).}
    • GISS: NASA Goddard Institute for Space Studies;
    • NCDC: NOAA National Climate Data Center;
    • CRU: Hadley Center / Climate Research Unit UK;
    • RSS: Remote Sensing Systems;
    • UAH: University of Alabama at Huntsville.
    (Foster and Rahmstorf, 2012)

    Increasing Ocean Heat Storage

    [Approximately] 93% of the additional heat absorbed by the Earth system resulting from an increase in greenhouse gas concentration since 1955 is stored in the ocean.
    (p 6)

    Between 1955 and 2010 the world’s oceans, to a depth of 2000 meters, have warmed on average by 0.09°C.

    Figure 4
    The increase in total ocean heat content from the surface to 2000 m, based on running five-year analyses.
    Reference period is 1955–2006.
    The black line shows the increasing heat content at depth (700 to 2000 m), illustrating a significant and rising trend, while most of the heat remains in the top 700 m of the ocean. …
    (Levitus et al, 2012)
    (p 7)

    Rising Sea Levels

    [Sea-level] rise of more than 20 cm [has occurred] since preindustrial times to 2009.
    The rate of sea-level rise was close to 1.7 [cm/decade] during the 20th century, accelerating to about 3.2 [cm/decade] on average since the beginning of the 1990s. …
    [For the period 1972-2008] the largest contributions have come from
    • thermal expansion [—] 0.8 cm/decade …
    • mountain glaciers, and ice caps [—] 0.7 cm/decade [and]
    • ice sheets [ie Greenland and Antarctica —] 0.4 cm/decade …
    The acceleration of sea-level rise over the last two decades is mostly explained by an increasing land-ice contribution from 1.1 cm/decade over 1972–2008 period to 1.7 cm/decade over 1993–2008 … because of the melting of the Greenland and Antarctic ice sheets …
    {[If] the present acceleration continues, the ice sheets alone could contribute up to 56 cm to sea-level rise by 2100.
    [Without] further acceleration, there [will] be a 13 cm contribution by 2100 from these ice sheets.}
    The [ratio] of land ice [to thermal expansion contributions to sea level rise] has increased by about a factor of three since the 1972–1992 period.

    Figure 5
    Global mean sea level (GMSL) reconstructed from tidegauge data (blue, red) and measured from satellite altimetry (black).
    The blue and red dashed envelopes indicate the uncertainty, which grows as one goes back in time, because of the decreasing number of tide gauges.
    (Church and White, 2011)

    Increasing Loss of Ice from Greenland and Antarctica

    Figure 6
    Left panel (a):
    The contributions of land ice (mountain glaciers and ice caps and Greenland and Antarctic ice sheets), thermosteric sealevel rise, and terrestrial storage (the net effects of groundwater extraction and dam building), as well as observations from tide gauges (since 1961) and satellite observations (since 1993).
    Right panel (b):
    [The] sum of the individual contributions approximates the observed sea-level rise since the 1970s.
    (Church et al, 2011)
    (p 8)

    [The] Greenland ice sheet moderately contributed to sea-level rise in the 1960s until early 1970s … was in balance until the early 1990s [and then] started losing mass again, more vigorously.
    (p 9)

    [Mass] loss from the Greenland ice sheet is presently equally shared between increased surface melting and increased dynamic ice discharge into the ocean. …

    Many marine-terminating glaciers have accelerated (near doubling of the flow speed) and retreated since the late 1990s.
    [These] retreats are triggered at the terminus of the glaciers, for example when a floating ice tongue breaks up. …

    There are indications that the greatest [surface] melt extent in the past 225 years has occurred in the last decade …

    Figure 9C
    Total ice sheet mass balance, dM/dt, between 1992 and 2010 for … the sum of Greenland and Antarctica, in Gt/year from the Mass Budget Method (MBM) (solid black circle) and GRACE time-variable gravity (solid red triangle), with associated error bars.
    (E Rignot, Velicogna, Broeke, Monaghan, and Lenaerts, 2011)
    (p 11)

    Ocean Acidification

    [The oceans] have taken up approximately 25% of anthropogenic CO2 emissions in the period 2000–06. …
    [The resulting ocean] acidification is occurring [along with an increase in water temperature] and a decrease in dissolved oxygen in the world’s oceans. …
    The rate of [observed] changes in overall ocean biogeochemistry [is] unparalleled in Earth history.

    Figure 11
    Observed changes in ocean acidity (pH) compared to concentration of carbon dioxide dissolved in seawater (p CO2) alongside the atmospheric CO2 record from 1956.
    A decrease in pH indicates an increase in acidity.
    (NOAA 2012, PM EL Carbon Program)

    Surface waters are typically supersaturated with aragonite (a mineral form of CaCO3), favoring the formation of shells and skeletons.
    If saturation levels are below a value of 1.0, the water is corrosive to pure aragonite and unprotected aragonite shells. …
    In upwelling areas, which are often biologically highly productive, undersaturation levels have been observed to be shallow enough for corrosive waters to be upwelled intermittently to the surface.
    (p 12)

    Loss of Arctic Sea Ice

    The linear trend of September sea ice extent since the beginning of the satellite record indicates a loss of 13% per decade …

    The area of thicker ice (that is, older than two years) is decreasing, making the entire ice cover more vulnerable to such weather events as the 2012 August storm, which broke the large area into smaller pieces that melted relatively rapidly. …

    [The] observed degree of extreme Arctic sea ice loss can only be explained by anthropogenic climate change.

    Figure 12
    Geographical overview of the record reduction in September’s sea ice extent compared to the median distribution for the period 1979–2000.
    (NASA, 2012)
    (p 13)

    Since the heat exchange between ocean and atmosphere increases as the ice disappears, large-scale wind patterns can change and extreme winters in Europe may become more frequent.
    (p 14)

    Drought and Aridity Trends

    [Warming] of the lower atmosphere strengthens the hydrologic cycle, mainly because warmer air can hold more water vapor.
    This strengthening causes dry regions to become drier and wet regions to become wetter …
    Increased atmospheric water vapor loading can also amplify extreme precipitation …
    {[Changes] in large-scale atmospheric circulation, such as a poleward migration of the mid-latitudinal storm tracks, can also strongly affect precipitation patterns.
    Warming leads to more evaporation and evapotranspiration, which enhances surface drying and, thereby, the intensity and duration of droughts.
    Aridity (that is, the degree to which a region lacks effective, life-promoting moisture) has increased since the 1970s by about 1.74% per decade, but natural cycles have played a role as well.}

    Observations covering the last 50 years [have confirmed] the intensification of the water cycle …
    [Indeed,] precipitation patterns over oceans [were affected at roughly] twice the rate predicted by the models.
    Over land, however, patterns of change are generally more complex because of aerosol forcing and regional phenomenon including soil and] moisture feedbacks. …
    [Nevertheless,] aerosol forcing has been linked to Sahel droughts.
    (p 14)

    [The Mediterranean] experienced 10 of [its] 12 driest winters [in the last century in] the last 20 years.
    Anthropogenic greenhouse gas and aerosol forcing are key causal factors [of] the downward winter precipitation trend in the Mediterranean. …

    East Africa has experienced a trend towards increased drought frequencies since the 1970s, linked to warmer sea surface temperatures in the Indian-Pacific warm pool, which are at least partly attributable to greenhouse gas forcing.

    [A] preliminary study of the Texas drought [of 2011 estimated that such events are now about] 20 times more likely [than they were] in the 1960s.

    [Attribution] of drought extremes remains highly challenging because of
    • limited observational data
    • the limited ability of models to capture meso-scale precipitation dynamics [and]
    • the influence of aerosols.

    Agricultural Impacts

    Since the 1960s … drought affected areas for maize [have increased] from 8.5 … to 18.6%.
    [Since] the 1980s … maize and wheat production [have declined] by 3.8% and 5.5%, respectively, compared to a model simulation without climate trends.
    [The] Russian heat wave in 2010 caused grain harvest losses of 25% …
    [This led] the Russian government to ban wheat exports [resulting in] $15 billion (about 1% gross domestic product) of total economic loss.

    [Extreme] temperatures can cause severe losses to agricultural yields …
    • Africa:
      [A] large number of maize trials … have found a particularly high sensitivity of yields to temperatures exceeding 30°C within the growing season.
    (p 15)

    • United States:
      [Significant] nonlinear effects are observed above local temperatures of 29°C for maize, 30°C for soybeans, and 32°C for cotton.

    • Australia:
      Large negative effects … have been found in Australia for regional warming variations of +2°C …

    • India:
      [Satellite] measurements of wheat growth in northern India [used] to estimate the effect of extreme heat above 34°C [have found that commonly used] crop models probably underestimate yield losses … by as much as 50% for some sowing dates …

    High impact regions are expected to be those where trends in temperature and precipitation go in opposite directions.
    One such “hotspot” region is the eastern Mediterranean where [crucial] wintertime precipitation … has been declining, largely because of increasing anthropogenic greenhouse gas and aerosol forcing.
    At the same time, summertime temperatures have been increasing steadily since the 1970s, [leading to further evaporative drying of] the soils …

    Figure 19
    Observed wintertime precipitation (blue), which contributes most to the annual budget, and summertime temperature (red), which is most important with respect to evaporative drying, with their long-term trend for the eastern Mediterranean region.

    Possible Mechanism for Extreme Event Synchronization

    The Russian heat wave and Pakistan flood in 2010 can serve as an example of synchronicity between extreme events.
    During these events, the Northern Hemisphere jet stream exhibited a strongly meandering pattern, which remained blocked for several weeks.
    Such events cause persistent and, therefore, potentially extreme weather conditions to prevail over unusually long time spans.

    These patterns are more likely to form when the latitudinal temperature gradient is small, resulting in a weak circumpolar vortex.
    This is just what occurred in 2003 as a result of anomalously high near-Arctic sea-surface temperatures.
    Ongoing melting of Arctic sea ice … has been linked to observed changes in the mid-latitudinal jet stream …
    (p 16)

    This could significantly [increase the risk of] extreme events occurring simultaneously in different regions of the world …
    [And if, for] instance, with three large areas of the world adversely affected by drought at the same time, there is a [significant] risk that agricultural production globally [would] not be able to compensate as it has in the past …

    Welfare Impacts

    [An analysis] of historical data for the period 1950 to 2003 [suggests] that climate change has adversely affected economic growth in poor countries in recent decades.
    [A] 1°C rise in regional temperature in a given year [reduced] economic growth in that year by about 1.3% …
    The effects on economic growth [were] felt throughout the economies of poor countries [and persisted] over 15-year time horizons. …
    (p 17)

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