[asa] John Houghton on AR4

Sir John Houghton is largely responsible for awakening evangelicals
to the need for action on climate change. Here's his assessment of
the latest AR4 SPM:

http://www.jri.org.uk/papers/IPCC_FAR_SPM_compared_to_TAR_7Feb2007.%
20doc.pdf

> Christians and Climate Change
> There follows a description of how many of the conclusions of the
> IPCC Third Assessment
> Report (TAR) of 2001 have been strengthened in the Fourth
> Assessment Report (FAR) of
> 2007. Confidence in the IPCC process should be enhanced by
> realising that the projections in
> the 1990, 1995 and 2001 reports of the global temperature rise
> expected in the near term in
> the range 0.15 to 0.3 deg C per decade compared well with what
> actually occurred of about
> 0.2 deg C per decade.

> With the stronger statements of the FAR, the reality of global
> warming due to human
> activities cannot now be denied. The severity of the likely
> resulting impacts brings great
> concern, especially through increased frequency and intensity of
> floods and droughts and of
> increased intensity of storms and tropical cyclones These are the
> most damaging on average
> of natural disasters that we experience. Recent work at climate
> modelling centres suggests a
> likely increase of the risk of floods and droughts in vulnerable
> areas of a factor of 5 or even
> more. This is bad news in all affected countries but especially bad
> news for poorer people in
> the most vulnerable countries in Africa, Asia and central America.
> Because of increased
> disasters together with problems due to sea level rise on low lying
> regions, by mid century
> hundreds of millions of environmental refugees will be looking for
> new areas to which to
> move in a increasingly crowded world.

> The Christian imperative to care for our poorer neighbours in other
> parts of the world is
> inescapable. The urgency for action is paramount - both to help our
> neighbours to adapt to
> climate change and to reduce our own carbon dioxide emissions at a
> rate that will slow and
> eventually halt climate change.

> IPCC Fourth Assessment Report (FAR), Summary for Policymakers
> Published 2 February 2007

> Its main messages compared with the Third Assessment Report (TAR)
> of 2001
> Additional information since the last IPCC Report six years ago has
> come from continuing
> and new observations and from advances in climate modelling.
> Simulations are now available
> from an increased number and wider range of models.

> In general, the conclusions of the FAR confirm and in many cases
> strengthen those of the
> TAR and earlier IPCC reports. In particular, since the IPCC’s first
> report in 1990, assessed
> projections have suggested global averaged temperature increases
> between about 0.15 and 0.3
> ºC per decade for the period 1990 to 2005. This can now be compared
> with observed values
> of about 0.2 ºC per decade over this period, strengthening
> confidence in these near term
> projections.

> Some of the conclusions which are updated or stronger than in the
> TAR are listed below.
> CO2 Emissions and Concentrations
> • An increase in emissions of CO2 from fossil fuel burning from 6.4
> GtC p.a. in the 1990s to
> 7.2 GtC p.a. from 2000-2005
> • Atmospheric CO2 concentration increased to 379 ppm by 2005,
> exceeding by far its natural
> range over the last 650,000 years. It is now increasing at an
> average 1.9 ppm p.a.
> Global Temperature Increase
> • Warming of the 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 mean sea level.
> • Most of the observed increase in globally averaged temperature
> since the mid-20th century is
> very likely (> 90% probability) due to the observed increase in
> anthropogenic greenhouse gas
> concentrations (the corresponding statement in the TAR said likely
> - meaning 67%
> probability). Discernible human influences now extend to other
> aspects of climate, including
> ocean warming, continental-average temperature, temperature
> extremes and wind patterns.
> • Analysis of climate models together with constraints from
> observations enables an assessed
> likely range to be given for climate sensitivity1 for the first
> time and provides increased
> confidence in the understanding of the climate system response to
> radiative forcing. Climate
> sensitivity is likely to be in the range 2 to 4.5 ºC with a best
> estimate of about 3ºC, and is very
> unlikely (< 10% probability) to be less than 1.5ºC. The TAR’s range
> for climate sensitivity
> was 1.5 – 4.5 ºC with a best estimate of about 2.5ºC and no
> assessment of probabilities of
> uncertainty levels.
> • Projections of global average temperature increases by 2090 -
> 2099 for the range of SRES
> scenarios are similar to those in the TAR, but presented separately
> for each scenario; for
> instance for the A1B scenario, the best estimate is 3ºC and the
> likely (probability 67%) range
> 1.7 to 4.4ºC.
> 1 Defined as the global average surface warming following a
> doubling of CO2 concentrations

> Sea Level Rise
> • Global average sea level rose at an average rate of 1.8 mm p.a.
> from 1961-2003. From 1993
> – 2003 the rate was faster, about 3.1 mm p.a. For 1993 – 2003, the
> sum of the estimated
> contributions from climate change (including contributions from
> losses from the ice sheets of
> Greenland and Antarctica) is consistent with the observed sea level
> rise.
> • 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.
> • Projections of sea level rise by 2090 – 2099 are consistent with
> those in the TAR although
> because of improved information about uncertainties the ranges are
> narrower. For instance for
> the A1B scenario, the range is 0.21 – 0.48 m (compared with 0.12 –
> 0.64 m in the TAR).
> These projections include a contribution due to increased flow from
> Greenland and Antarctica
> at the rates observed for 1993-2003, but they do not include the
> full effects of changes in ice
> sheet flow because a basis in the published literature is lacking.
> For example, if this
> contribution were to grow linearly with global average temperature
> change, the upper ranges
> of sea level rise for SRES scenarios would increase by 0.1 – 0.2 m.

> Climate extremes
> • Continuing with observed trends, it is very likely (> 90%
> probability) that hot extremes, heat
> waves and heavy precipitation events will continue to become more
> frequent. It is likely (>
> 67% probability) that the area affected by drought will increase.
> • Increases in the amount of precipitation are very likely (> 90%
> probability) at high latitudes
> while decreases are likely (> 67% probability) in most sub tropical
> land regions (by as much
> as about 20% in the A1B scenario in 2100) continuing observed
> patterns in recent trends.
> • It is likely (> 67% probability) 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 sea surface temperature.

> Regional Climate Change
> • There has been substantial improvement since the TAR in model
> projections of regional
> climate change. For instance, projected warming during the 21st
> century shows scenarioindependent
> geographical patterns similar to those observed in recent decades.
> Warming is
> expected to be greatest over land and at most high latitudes.
> • Sea ice is projected to shrink in both the Arctic and the
> Antarctic. In some projections Arctic
> late-summer sea ice disappears almost entirely by the latter part
> of the 21st century.

> Commitment already to Climate Change
> • Climate Change cannot immediately be switched off. Even if all
> climate forcings were held
> constant (e.g. greenhouse gas emissions were terminated) at year
> 2000 levels, a further
> warming trend would occur in the next two decades of about 0.1ºC
> per decade, due mainly to
> the slow response of the oceans.

> John Houghton
> 12 February 2007

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Received on Sun Mar 4 18:12:11 2007