Positive effects of warming
43. The Committee noted that the scientific literature tended
to focus on the negative impacts of climate change. This is understandable
given that some of these effects are thought to be catastrophic,
and because individuals tend to be more averse to a loss than
they are in favour of an equivalent gain.
But a rigorous appraisal of climate change does need to include
positive effects. The beneficial effects of CO2 "fertilisation"
on crops was noted above. But there will also be gains in amenity
across large areas. Several studies were presented to us which
indicated the nature of some of these amenity gains: increased
opportunities for tourism, for example, but also the fact that
many people simply prefer to live in mild climates. In his evidence,
Professor Mendelsohn of Yale University argued that regions have
"optimal" climates: regions that are "too cold"
gain from warming, while those that are "too hot" will
lose. Dr David Maddison
of University College London and Ms Katrin Rehdanz of Hamburg
University argue that impacts at the level of the household will
be the most profound, yet little is known about how households
perceive climate change. Like Professor Mendelsohn, they invoke
the notion of an optimal climate but at the household level, with
households moving towards or away from that optimum as climate
change occurs. The
research suggests that people will accept lower wages to work
in areas of "better" climate typified by lower rainfall,
lower mid-summer temperatures (in countries such as Italy) and
lower cloud cover. Similarly, house prices tend to be higher in
regions with preferred climates. Household expenditures also change
with climate. Finally, individuals' own ratings of their "happiness"
have been shown to vary directly with income and climate.
Overall, there appear to be distinct amenity gains for the countries
of Northern Europe, with generally neutral effects in Southern
Europe. Once the focus moves to Asia there are serious household
losses, confirming the general picture that it is the poorer parts
of the world that suffer most from warming. We are clear that
fuller consideration needs to be given to the literature on the
positive effects of warming.
44. We draw attention to this literature for several reasons.
First, we heard little about the positive effects of warming from
the scientific witnesses. Second, we observe that this category
of benefit is mentioned only in passing in the IPCC Working Group
II assessment of impacts, where it is noted that economic impact
studies "may have overlooked" positive impacts.
We conclude that there are weaknesses in the way the scientific
community, and the IPCC in particular, treats the impacts of climate
change. We call for a more balanced approach and look to the Government
to take an active role in securing that balance of research and
Adaptation versus mitigation
45. The IPCC 2001 Reports make explicit reference to adaptation
to climate change. Adaptation can take various forms. The IPCC
reports distinguish "autonomous" and "planned"
adaptation. First, market forces and natural behaviour will lead
to some "natural" adaptation to climate change, e.g.
by changing crop strains so that crops are more tolerant of dry
conditions. Second, conscious and deliberate policies and investments
will also be needed to encourage further adaptation. We understand
the IPCC cautions on adaptation: it is easy to see that reliance
on adaptation alone would be risky since it may not be possible
to adapt to major risks. But it also seems to us that nearly all
of the public debate on global warming is about mitigationreducing
emissionsrather than about adapting to climate change and,
assisting the most vulnerable societies in the world to adapt
to the risk they may face.
46. In evidence to us, Dr Indur Goklany of the US Department
of the Interior argued that mitigation can do little to reduce
many of the impacts from warming, whereas investment in adaptation
now would both reduce the baseline risks that will occur even
without any warming, and the warming impacts as well. His estimates
suggest that warming could add substantially to the population
at risk, notably from hunger, water shortage and coastal flooding.
Those at risk from additional water shortage could, however, be
offset by those who benefit because of warming-induced water gains.
47. The issue is clearly one of balance. Most adaptation
expenditures would be local, while mitigation requires action
on a global scale. Few would suggest doing nothing by way of mitigation,
and few would suggest no adaptation expenditures at all. But the
policy literature seems to us to be overly focussed on mitigation.
We therefore urge the Government to ensure that greater efforts
are made to understand the relative costs and benefits of adaptation
compared to those of mitigation.
23 Detailed assessments of the likely impacts can
be found in Inter Governmental Panel on Climate Change, Climate
Change 2001: Impacts, Adaptation, and Vulnerability. Cambridge:
Cambridge University Press, 2001. Back
J. Houghton et al. Climate Change 2001: The Scientific Basis.
Contribution of Working Group I to the Third Assessment Report
of the Intergovernmental Panel on Climate Change. Cambridge:
Cambridge University Press. 2001. The benchmark for these temperature
increases is not always clear, but is usually the "pre-industrial"
period, i.e. around 1750. Thus, a projected rise of, say, 2.60C
would imply warming of about 20C compared to the present
day. Some of the scientific opinion at the conference convened
in Exeter early in 2005 considered that the IPCC 2001 Assessment
understates likely temperature change. Back
Evidence of Professor Colin Robinson (Vol II, pp 1-14) Back
R. Watson et al. op.cit. p.182 Back
In many cases, reducing greenhouse gas emissions also reduces
other pollutants, such as particulate matter. For example, any
reduced road transport would have this effect since particulates
and CO2 are emitted from vehicles. The benefits of
reducing particulates would, however, be fairly immediate. This
joint effect is known as "ancillary benefits" in the
literature. However, if the pollutant reduced is sulphur, then
reduced sulphur emissions may actually increase warming-see the
section on "negative forcing". Back
R. Watson et al. op.cit. p.256 Back
P. Stott, D. Stone and M. Allen, Human contribution to the European
heatwave of 2003. Nature, 432,
2 December 2004, 610-613. Back
Evidence of P. Reiter: The IPCC and Technical Information. Example:
Impacts on Human Health (Vol II pp 284-288) Back
See R. Watson et al. op.cit. p.223. In his evidence to us (Vol
II, pp 96-106), Sir David King was clear that current evidence
suggests glaciers are in retreat for the first time in the current
warming period. Back
The Guardian, 2 April 2005, reporting evidence from Dove
Marine Laboratory, Newcastle University. Back
R. Watson et al. op.cit. p.231 Back
M. Parry et al. Viewpoint. Millions at risk: defining critical
climate change threats and targets. Global Environmental Change.
11, 2001. 181-3 Back
Sir John Houghton, Global Warming: The Complete Briefing.
Third Edition. 2005. Cambridge: Cambridge University Press. P179. Back
R. Watson et al. op.cit. p256. Back
M. Khandekar . Are climate model projections reliable enough
for climate policy? Energy and Environment, 15 March 2004 Back
For an overview of these features see J. Rial et al. Nonlinearities,
feedbacks and critical thresholds within the Earth's climate system.
Climatic Change. 65. 2004. 11-38. Back
See M. Maslin, Global Warming: a Very Short Introduction.
Oxford: Oxford University Press. 2004. Back
In his evidence to us (Vol II, pp 96-106), Sir David King thought
this shut-down process might take only a decade and that the temperature
fall might be -200C. Back
These gas hydrates also exist in vast reserves below the world's
oceans. There is a scientific debate about the extent to which
high warming levels could also begin to release these hydrates,
something that does appear to have happened many millions of years
M. Parry et al. op.cit. Back
This phenomenon of "loss aversion" is well documented
in the psychological and economics literature. Back
Evidence from R. Mendelsohn (Vol II, pp 266-269). See also R.
Mendelsohn and M. Schlesinger, Climate response functions.
Ambio, 28, 1999, 362-6 Back
Evidence from D. Maddison (Vol II, pp 256-262). Back
K. Rehdanz and D. Maddison. Climate change and happiness. Ecological
Economics. 52. 2005. 111-125. Back
There is no chapter or sub-section of the IPCC Working Group
II 2001 Report dealing with positive impacts. Chapter 19 lists
positive effects in the agricultural sector and possible reductions
in winter mortality but makes no mention of amenity effects. Back
Evidence from I. Goklany (Vol II, pp 217-225). Back