The Lancet, Volume 384, Issue 9948, Pages 1073 - 1075, 20 September 2014
Copyright © 2014 Elsevier Ltd All rights reserved.
Health risks of climate change: act now or pay later
There
is growing scientific consensus that climate change is happening, is
largely human induced, and will have serious consequences for human
health. The impact of climate change on global health is probably not
yet large, compared with major risk factors, but will become greater
later in this century, especially if the world follows one of the
so-called high-end emission pathways, such as Representative
Concentration Pathway (RCP) 8·5, outlined in the UN Intergovernmental
Panel on Climate Change (IPCC) Fifth Assessment Report.1, 2
This
emission pathway assumes that present trends of relatively unrestrained
use of fossil fuels and high population growth will continue. According
to this emission pathway, by 2100 the global average temperature will
probably be more than 4°C above preindustrial levels (figure),
with higher average temperatures over land. Inertia in climate systems
would mean that projected global temperatures would continue to rise for
several hundred years; the mean estimate for this emission pathway in
2300 would be at least 8°C above preindustrial levels. Long-term global
average warming of 12°C or more is possible from unconstrained fossil
fuel burning. An increase of 12°C in global average temperature would
create conditions in which physiological limits for outdoor activity
would be reached during certain times of the year in many heavily
populated parts of the world.3
One study estimates that under RCP 8·5 there would be about a 40%
reduction in global labour capacity during the hottest months by 2100.4
Figure Full-size image (39K) Download to PowerPoint
Projected global mean surface temperature change to 2100 compared with 1850—1900
Pathways
showing differences in future world temperatures with differing degrees
of control for carbon dioxide and other greenhouse pollutants. The
temperature changes from the RCPs are derived from figures SPM.7, 12.5,
TS.15, table 12.2 in the IPCC's Fifth Assessment Report.1
Based on combining the results of many independent models, the high-end
emission pathway, RCP 8·5, shows the range of what is likely to occur
with current trends of modest emissions controls together with
continuing population growth and slow technological and economic
progress. The low emission pathway, RCP 2·6, reflects the range with
much greater greenhouse control actions started soon. Although the
differences in temperature between the two RCPs during the early part of
the century are modest, they diverge widely after mid-century,
indicating the importance of acting quickly. Importantly, unlike
pathways that include aggressive control measures, under the high-end
emission pathway the climate does not reach stability even by 2100 when
global temperature is still increasing about 0·7°C per decade. Finally,
at any mean global temperature rise, over land and in high latitudes the
changes would be higher. Under pathway RCP 8·5, by 2100 the mean
increase over land is projected to be about 1·1°C higher than shown in
the figure. In parts of the Arctic mean temperature increases could
reach 12°C from baseline by 2100 under the same high-end emission
pathway. Dotted horizontal line represents baseline average temperature
between 1850 and 1900. RCP=Representative Concentration Pathway.
The
effects of climate change on humanity under such high-end emission
scenarios are difficult to estimate. No epidemiology is possible, models
cannot be validated, and baseline world health and socioeconomic
conditions that far into the future are a matter close to conjecture.
However, such extreme temperature trends might cross what has been
called the “afterlife” threshold—ie, where the impact on humanity is so
great as to be a discontinuity in the long-term progression of humanity.5
The
climate implications of different emission trajectories will not
strongly diverge until the middle of the 21st century, whatever progress
is achieved in the next few decades in reducing greenhouse-gas
emissions. Therefore, the near-term and medium-term (up to about 2050)
is a time to promote and fund adaptation measures that will reduce the
damage to health caused by climate change, to which the world is already
committed. Society also needs to prepare for the possibility of more
serious changes later in the century. For example, in the next 20—30
years, net global food production might be maintained as a result of
increased crop yields in cooler, high latitudes. However, continued
warming after 2050 would adversely affect crop yields in most parts of
the world, at a time when demand for food will be rising strongly due to
projected population growth and economic development.6
Both
a high absolute level and a rapid rate of global climate change will
severely test biological and social mechanisms for adaptation, with
limits to adaptation becoming increasingly evident. Examples range from
emergency preparedness in the face of shortening return periods after
potentially catastrophic floods, to saltwater intrusion into freshwater
lenses in small islands which would potentially compromise water quality
to such an extent that migration might be the only option.7
Furthermore, limits to adaptation will arise when hazards associated
with a changing climate interact with inappropriate development
pathways—eg, where building occurs on flood plains. Adaptation limits
might also occur when health systems fail to proactively design and
implement adaptation actions needed to address a particular health risk.
The need to strengthen health-system capacity in low-income countries
to prepare for, cope with, and recover as far as possible from the
health effects of climate change that do occur could be partly addressed
by equitable partnerships between high-income and low-income countries.
The
health community has a role in the promotion of policies to reduce
emissions of all climate-active pollutants, both because many of these
pollutants are health hazards now and because all push the climate
towards possible extremes within this century. Major reductions in
mortality would ensue from measures to reduce combustion of
carbon-containing fuel and consequent carbon dioxide and fine particle
emissions, for example by curbing coal combustion. Furthermore, there
are co-benefits for both health and climate from actions to reduce
short-lived climate pollutants, such as black carbon and methane, the
second most important greenhouse gas and the primary precursor to ozone
in the lower atmosphere.8, 9
Provision of wider access to reproductive health services could also
reduce carbon dioxide emissions over the century and improve maternal
and child health.10
Wise
policies to develop low-emission economies that use the full range of
available technological options would provide many societal benefits and
only have moderate impacts on economic growth projections.9 Nevertheless, such changes tend to be opposed by those with a stake in current economic pathways.
The
burden of disease and injury due to climate change falls mainly on
specific vulnerable groups, particularly those living in poverty.
Vulnerability to climate change is in many cases inversely related to
historical greenhouse gas emissions. Thus, the responsibility for
leading policies to reduce these emissions should be shouldered by those
nations and commercial interests that have enjoyed the benefits of
fossil-fuel-driven development. Since emerging economies are responsible
for a growing proportion of emissions, however, they too must move
towards development with low greenhouse gas emissions, which some are
starting to do.
The timescale is daunting
but not a reason for inaction: the health community needs to argue for a
long-term perspective on climate change. Article 2 of the United
Nations Framework Convention on Climate Change states that the objective
is to avoid dangerous anthropogenic interference with the Earth's
climate.11
Without decisive action this objective cannot be achieved. The world's
carbon budget to keep global increases in temperature below 2°C is
likely to be exceeded by 2040.9
Society must, therefore, enhance efforts to adapt to reduce adverse
effects on human health, particularly for the most vulnerable. The
prospect of extreme climates beyond mid-century, however, should impel
the health community to promote deep cuts in emissions of climate-active
pollutants now for the long-term protection of human welfare, starting
with co-benefit actions that protect both health and climate.
The
authors were members of the UN Intergovernmental Panel on Climate
Change Fifth Assessment Report and contributed to chapter 11 on human
health. This Comment represents their own views and not necessarily
those of the UN Intergovernmental Panel on Climate Change.
References
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people, places and planet: reflections based on Tony McMichael's four
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9 In: Edenhofer O, Pichs-Madruga R, Sokona Y, et al, eds. IPCC,
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of Working Group III to the Fifth Assessment Report of the
Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press, 2014. http://report.mitigation2014.org/drafts/final-draft-postplenary/ipcc_wg3_ar5_final-draft_postplenary_full.pdf. (accessed Sept 15, 2014).
10 . Demographic change and carbon dioxide emissions. Lancet 2012; 380: 157-164.
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11 . Article 2 objective. http://unfccc.int/essential_background/convention/background/items/1353.php. (accessed Sept 7, 2014).
a
Departments of Social and Environmental Health Research and Population
Health, London School of Hygiene & Tropical Medicine, London WC1H
9SH, UK
b Department of Global Health, University of Washington, Seattle, WA, USA
c School of Public Health, University of California Berkeley, Berkeley, CA, USA
d School of Population Health, University of Auckland, Auckland, New Zealand
