The Science of
Climate Change
Questions and
Answers
August 2010
The Science of Climate Change
, Prof. Kurt Lambeck political models each with their own inherent they are authoritative within the current state of
President, Australian assumptions and difficulties with data and knowledge. This Committee consists of eminent
Academy of Science observations. In the presence of uncertain Fellows of the Academy and other experts with
May 2006 – May 2010 scientific uncertainty, it should not be surprising both extensive research experience in related
Foreword
that, when it comes to recommendations about fields and in the leadership of climate-related
Summary
how to respond to a threat of climate change, programs and organisations.
the spectrum of opinions is broad indeed. While it is important to emphasise that it is
The Australian Academy of Science is not possible to provide definitive answers to
strongly committed to enhancing public many of the questions that are being asked
T
he science of climate is at the intersection understanding of scientific issues and how about climate change, it is also important to
of a number of science disciplines and these may impact on society and the planet. stress that considerable progress has been
T
sub-disciplines. At its heart are physics, Through its members and through its National made in understanding climate change and he Earth’s climate has changed. The
chemistry, biology and mathematics – each with Committees for Science it is able to draw on why it occurs. The role of greenhouse gases in global average surface temperature
their sub-disciplines of atmospheric physics and expertise from across a broad sector of the the atmosphere is qualitatively well understood.
chemistry, oceanography, hydrology, geology Australian science community to report on It is known that increasing the atmospheric
has increased over the last century
etc – and each of which can be considered important scientific issues. concentration of the principal anthropogenic and many other associated changes have been
as mature within the framework required to This includes climate science. The Academy greenhouse gas, CO2, leads to higher mean observed. The available evidence implies
discuss climate. It is at this intersection of the recognises that decisions on how to respond global surface temperatures. It is known that that greenhouse gas emissions from human
disciplines where uncertainty can and will arise, to climate change will have to be made by our CO2 has increased very substantially during activities are the main cause. It is expected
both because of the yet poorly understood society as a whole. These decisions need to the last century, to the highest levels seen in that, if greenhouse gas emissions continue at
feedbacks between the different components consider the findings of climate change together the past 800,000 years, and that this increase business-as-usual rates, global temperatures
of the climate system and because of the with many considerations that go beyond the is primarily of anthropogenic origin. It is also will further increase significantly over the
difficulty of bringing these components together science and must include, amongst others, beyond serious question that some CO2 from
into a single descriptive and predictive model. ethics and equity, economics, risk management human activities remains in the atmosphere for
coming century and beyond.
This would include, for example, the biological and politics. The purpose of this document a very long time, as is the message that unless The science behind these statements is
consequences of how increasing carbon dioxide is to contribute to the public understanding greenhouse gas emissions are reduced, an supported by extensive studies based on four
(CO2) feeds back into climate and into the of the state of the science and to attempt to upward trend in global temperature will continue. main lines of evidence:
climate model, or how the consequences of tread a path through the often contradictory The uncertainties in the science do not affect
atmospheric warming on water vapour, cloud public commentary on the science. It is not a such major conclusions but they will affect the Physical principles established more than a
cover, ocean warming and circulation feedback formulation of a policy response but an attempt precise timescales or magnitudes of the change century ago tell us that greenhouse gases, such
can be described and quantified in a coherent to improve the public understanding of the and they will affect the global distribution of its
and integrated theory. It is these feedbacks and science upon which any policy response should impact. It is important therefore that extensive
as carbon dioxide (CO2), trap heat and keep
interactions that make it difficult to realistically be constructed. research and rigorous scientific debate continue the planet warmer than it would otherwise
quantify the uncertainty in the outputs of climate To this effect the Academy’s Council within the expert scientific community and be. Increasing greenhouse gas levels raise the
models at levels that the experimental scientist established two committees to address some that the communication of that research to the temperature of the Earth’s surface.
is usually accustomed to. In a process as of the major questions that are frequently broader community be effective. The Academy
intrinsically complex as climate it should not be asked about climate change science. First, therefore hopes that this report will provide a The record of the distant past (millions
surprising that the path to understanding is long an expert Working Group carefully formulated firmer basis for understanding the science of of years) tells us that we cannot take a stable
and arduous. the questions and answers about the science climate change and its implications.
climate for granted. Climate has varied
In many other areas of experimental science of climate change. This group consists of The Academy is very appreciative of
the paths to full understanding are equally internationally recognised scientists who have the contributions made to this report by the
greatly through the Earth’s history. It has, for
complex. What makes climate change different contributed extensively to the underpinning members of the Working Group and Oversight example, gone through 10 major ice age cycles
is that the consequences are not only potentially science, including contribution to the successive Committee to provide authoritative answers to over approximately the past million years. The
global and serious but also that they occur IPCC assessments. Seven ‘big’ questions were these important questions on the science of past few thousand years have been unusually
over long time scales (decades to centuries) identified within each of which ‘lower-level’ climate change. The Academy also thanks the stable. Together with our understanding of
so that actions need to be contemplated before questions have also been addressed. Second, Department of Climate Change and Energy
full understanding is achieved. These actions an Oversight Committee comprehensively Efficiency for providing financial support to
themselves are built on economic, social and reviewed the answers provided to ensure that prepare this document.
Published by the Australian Academy of Science; ISBN 085847 286 4. Please cite “The Science of Climate Change: Questions and Answers”, Australian Academy
of Science, Canberra.
The Science of Climate Change
, physical principles, evidence from the past
shows that climate can be sensitive to small
external influences.
spells, changes to rainfall patterns and a
higher global average rainfall, higher plant
productivity in some places but decreases T
his document aims to summarise
and clarify the current
understanding of the science
4 Are human activities causing
climate change?
Human activities are increasing greenhouse
in others, disturbances to marine and of climate change for non-specialist gas levels in the atmosphere. It is very
Measurements from the recent past terrestrial ecosystems and biodiversity, readers. The document is structured likely that most of the recent observed
(the last 100 years) tell us that the Earth’s disruption to food production in some around seven questions. global warming is caused by this increase
surface is warming along with rising regions, rising sea levels, and decreases in in greenhouse gases.
levels of greenhouse gases from human
activities, and that this warming is leading
to other environmental changes. Although
Arctic ice cover. While aspects of these
changes may be beneficial in some regions,
the overall impacts are likely to be negative
1 What is climate change?
Climate is a statistical description
of weather conditions and their variations, 5 How do we expect climate to
evolve in the future?
climate varies from year to year and decade under the present structure of global society. including both averages and extremes. Climate models and studies of past climates
to decade, the overall upward trend of A warming of 7°C would greatly Climate change is a change in the average indicate that global warming and associated
average global temperature over the last transform the world from the one we pattern of weather over a long period of changes will continue if greenhouse gas levels
century is clear. now inhabit, with all of the above impacts time. Greenhouse gases play an important keep rising as they are now. It is very likely
being very much larger. Such a large and role in determining climate and causing there will be significant warming through the
Climate models, together with physical rapid change in climate would likely be climate change. 21st century and beyond. Reduction of
principles and knowledge of past beyond the adaptive capacity of many greenhouse gas emissions could significantly
variations, tell us that, unless greenhouse
gas emissions are reduced and greenhouse
societies and species.
There are uncertainties in climate science. 2 How has Earth’s climate
changed in the distant past?
reduce long-term warming.
gas concentrations in the atmosphere are
stabilised, global warming will continue.
For example, a precise value cannot be
given for the likely range of warming
because of uncertainties in climate sensitivity
Global climate has varied enormously
through Earth’s history. Evidence from the
past shows that global climate can be sensitive
6 What are the consequences
of climate change?
Climate change will have significant impacts
Climate models estimate that, by 2100, to small disturbances, although climate to small influences. Past records also on our society and environment, both directly
the average global temperature will be models and evidence from past climate change show that climates can shift abruptly. and by altering the impacts of other stresses.
between 2°C and 7°C higher than pre- provide a plausible range of values. Climate
industrial temperatures, depending on future
greenhouse gas emissions and on the ways
that models represent the sensitivity of climate
changes over small regions and changes in
rainfall patterns are very hard to estimate.
Tipping points or rapid climate transitions
3 How has climate changed
during the recent past?
Global average temperature has increased
7 How do we deal with the
uncertainty in the science?
Although climate forecasts are uncertain and
to small disturbances. Models also estimate associated with overall global warming are over the past century. Evidence for this comes will remain so, the broad conclusions of climate
that this climate change will continue well possible but cannot yet be predicted with from instrumental temperature records in the change science as outlined above are based on
after 2100. confidence. These uncertainties work in both air and the ocean. Temperature observations many lines of evidence which together give a
A 2°C global warming would lead to directions: there is a chance that climate are not the only evidence of recent climate high degree of confidence. Partly because of
a significantly different world from the change will be less severe than the current change: other sources include trends in sea scientific uncertainty but also because many
one we now inhabit. Likely consequences estimates of climate science, but there is also a levels, glaciers, ice caps and atmospheric aspects of human life are involved, decisions
would include more heat waves, fewer cold chance that it will be more severe. water vapour that are consistent with global about action on climate change will need
warming. Australia’s climate has changed to involve extensive consideration of issues
along with global climate. beyond science, including ethics, economics
and risk management.
The Science of Climate Change
