In a recent blog entry, I discussed why professional societies should issue position papers on issues of public importance. That was the topic of an exchange of letters to Physics Today, including mine. Now, as if to emphasize my reasoning, the UK Royal Society has published an excellent and informative 16-page summary of the scientific issues surrounding climate change for general readers.
That report begins with a section of background on climate and climate science. It then has a section describing “Aspects of climate change on which there is wide agreement.” Following that is “Aspects of climate change where there is a wide consensus but continuing debate and discussion. Next comes “Aspects that are not well understood,” followed by developments in climate science, concluding remarks, background reading, and acknowledgments.
As a scientist, I am most pleased that the report enables non-scientists an opportunity to see how scientists draw conclusions based on evidence, consider dissenting interpretations, and develop a consensus view with clearly stated strengths and limitations.
However, knowing that many of you want just a summary of that summary report, here are the section headings. I also include some excerpts:
Climate and climate change: some background science
The greenhouse effect
Mechanisms of global climate change
Modelling the climate system
Changes in global-average surface temperature
Other changes in climate
Aspects of climate change on which there is wide agreement
Changes in atmospheric composition
Climate forcing by greenhouse gas changes
Carbon dioxide and climate
Aspects of climate change where there is a wide consensus but continuing debate and discussion
The carbon cycle and climate
Other drivers of global climate change
[NOTE: These include:
* Volcanic eruptions
* Natural forcing due to sustained variations in the energy emitted by the Sun
* Human activity]
Attribution of climate change
The size and sustained nature of the observed global-average surface warming on
decadal and longer timescales greatly exceeds the internal climate variability simulated
by the complex climate models. Unless this variability has been grossly underestimated,
the observed climate change must result from natural and/or human-induced climate
When only natural climate forcings are put into climate models, the models are
incapable of reproducing the size of the observed increase in global-average surface
temperatures over the past 50 years. However, when the models include estimates of
forcings resulting from human activity, they can reproduce the increase. The same
result is found, albeit with a greater spread between different models, for the simulation
of observed surface temperature changes for each of the habitable continents
When known uncertainties in both observed trends and climate models are taken into
account, the observed vertical and latitudinal variations of temperature change are also
broadly consistent with those expected from a dominant role for human activity. There
is an ongoing controversy concerning whether or not the increased warming with
height in the tropical regions given by climate models is supported by satellite
Future climate change
As with almost any attempts to forecast future conditions, projections of future climate
change depend on a number of factors. Future emissions due to human activity will
depend on social, technological and population changes which cannot be known with
confidence. The underlying uncertainties in climate science and the inability to predict
precisely the size of future natural climate forcing mechanisms mean that projections
must be made which take into account the range of uncertainties across these different
Aspects that are not well understood
There is currently insufficient understanding of the enhanced melting and retreat of the
ice sheets on Greenland and West Antarctica to predict exactly how much the rate of
sea level rise will increase above that observed in the past century (see paragraph 45)
for a given temperature increase. Similarly, the possibility of large changes in the
circulation of the North Atlantic Ocean cannot be assessed with confidence. The latter
limits the ability to predict with confidence what changes in climate will occur in
[NOTE: I consider this to be the most significant uncertainty, and I reviewed a book that speculates what might happen if the melting is much greater than projected.]
Developments in climate science
Climate change science has advanced markedly over the past 20 years, as a result of
many factors. These include improved methods for handling long-term climate data
sets, the ever-lengthening record of climate observations, improved measurement
techniques, including those from satellites, better understanding of the climate system,
improved methods for simulating the climate system, and increased computer power.
One indication of these advances is the increasing degree of confidence in the
attribution of climate change to human activity, as expressed in the key conclusions of
IPCC Working Group 1 (WG1) in its assessments.
Remaining uncertainties are the subject of ongoing research worldwide….
There remains the possibility that hitherto unknown aspects of the climate and climate
change could emerge and lead to significant modifications in our understanding.
Concluding remarks [Note: This section is reproduced in full]
There is strong evidence that changes in greenhouse gas concentrations due to human
activity are the dominant cause of the global warming that has taken place over the last
half century. This warming trend is expected to continue as are changes in precipitation
over the long term in many regions. Further and more rapid increases in sea level are
likely which will have profound implications for coastal communities and ecosystems.
It is not possible to determine exactly how much the Earth will warm or exactly how the
climate will change in the future, but careful estimates of potential changes and
associated uncertainties have been made. Scientists continue to work to narrow these
areas of uncertainty. Uncertainty can work both ways, since the changes and their
impacts may be either smaller or larger than those projected.
Like many important decisions, policy choices about climate change have to be made in
the absence of perfect knowledge. Even if the remaining uncertainties were
substantially resolved, the wide variety of interests, cultures and beliefs in society would
make consensus about such choices difficult to achieve. However, the potential impacts
of climate change are sufficiently serious that important decisions will need to be made.
Climate science – including the substantial body of knowledge that is already well
established, and the results of future research – is the essential basis for future climate
projections and planning, and must be a vital component of public reasoning in this
complex and challenging area.