Twenty-eighth Report Adapting Institutions to Climate Change Cm ...

Chapter 2
2.10
2.11
2.12
2.13
2.14
Since the late 19th century to the present day, global average temperatures have risen by 0.8°C.
But the rate of warming is accelerating and in the last 25 years global average temperatures have
risen at a rate of 0.2°C per decade. According to the Met Office, the 17 warmest years on record
have all occurred in the last 20 years, and the warmest year so far has been 1998, 6 due in part to
the global effects of a strong El Niño ocean-warming event. i The Intergovernmental Panel on
Climate Change (IPCC) has concluded that it is ‘very likely’ ii that man-made greenhouse gas
(GHG) emissions have caused most of the observed temperature rise since the mid-20th century. 7
This view is widely shared by the leading scientific institutions throughout the world.
As the climate warms, snow cover, the extent of sea ice and some land-based ice sheets and glaciers
are declining worldwide. Recorded observations show that global average sea levels have been
rising since at least 1870; the rise is accelerating. Global average sea levels have risen since 1961
at an average rate of 1.8 mm per year and since 1993 at about 3 mm per year, with contributions
from ocean thermal expansion and melting glaciers, ice caps and polar ice sheets. 8 Variations in
the geological movement in land will mean that local rates of sea level rise will themselves vary.
For example, net sea level rise will be greatest in south-east England, where the land is sinking,
and least in Scotland, where it is rising (2.72).
In 2005, the atmospheric carbon dioxide level was 379 ppm and rising at approximately 2 ppm
per year. 9 The IPCC predicts that if atmospheric carbon dioxide levels continue to rise, and
double from a pre-industrial concentration of 280 ppm, increases in the equilibrium global
mean surface air temperature are ‘likely’ (see footnote vi) to be in the range 2.0-4.5°C, with a
most likely value of about 3°C. However, temperature increases substantially higher than 4.5°C
still cannot be excluded (although this carries a lower probability). 10 Increasing global average
temperatures will have a pronounced impact on local weather. Commenting on future extremes
of temperature, the IPCC stated it is ‘very likely’ that heatwaves will become more intense, more
frequent and longer lasting. 11
Heatwaves are prolonged periods of excessively hot weather which may be accompanied by
high humidity that can cause serious health problems. As part of the Heat-Health Watch system
operating in England and Wales from 1 June to 15 September each year, 12 heatwave alerts are
issued when temperatures reach a certain threshold and are sustained over two days and the
intervening night, with a forecast of higher temperatures to come. The temperature threshold
will vary according to region – for example, in London the daytime threshold is 32°C and 18°C at
night, whereas for the north-west of England the thresholds are 30°C and 15°C respectively.
Precipitation patterns (rain and snowfall) are also changing so that at tropical and higher latitudes,
both average precipitation and the intensity of rainstorms are predicted to increase because of
a general intensification of the global hydrological cycle. An increased risk of fluvial and urban
flooding is one consequence of more frequent and more intense rainfall.
i The El Niño phenomenon is a warm phase of a natural oscillation in the Earth’s climate system. Involving both
ocean and atmosphere, it occurs when the tropical surface waters of the Pacific Ocean warm, the westward trade
winds slacken and the region of strongest rainfall moves eastwards from Indonesia out into the Pacific Ocean.
Although not totally predictable, it tends to occur on average every four years, lasting for about 12-18 months.
ii IPCC terminology expresses likelihoods thus: ‘very likely’ = >90% probability; ‘likely’ = >66% probability.
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