Thank you very much.
Thank you for the opportunity to be a witness.
I'll start by describing a little bit about the IPCC assessment process. I have a heavy involvement in the IPCC. I'm a vice-chair of the IPCC bureau, as Professor Stone has been in the past.
The principal products of the IPCC are sets of comprehensive reports, issued roughly every six years, on the science of climate change, impacts, adaptation and vulnerability, and the mitigation of climate change, together with a synthesis report.
The process is one that engages governments and in which governments take ownership. The scientific community, together with input from the governments, develops a proposed outline for the report and that outline is then approved by the member countries. There are currently 194 member countries of the IPCC.
The governments commission a particular type of report. The world's top scientists then assess the available literature. The IPCC does not do research, but produces draft reports that are reviewed extensively.
In the case of Working Group 1, in which I was involved, there were more than 30,000 comments from scientists and government analysts of all stripes. Authors are required to respond to each and every one of those comments. There are review editors who track how those responses are produced to ensure that responses are provided in a fulsome manner.
Ultimately, the governments accept the reports that are produced and give line-by-line approval of the summaries for policy-makers, again making the reports theirs. These are 194 governments of all stripes, from all over the world.
Canada makes important contributions to the IPCC, providing both leadership and expertise for the assessment process. As I mentioned, Canada sits on the IPCC bureau. We provide expertise from government labs, universities, and the private sector and we undertake substantial amounts of science in this country.
On the key findings from the IPCC, there are two, in essence. The first is that the IPCC concluded in its fourth assessment report that the world is warming, that human activities are largely responsible for this warming, and that additional warming is inevitable.
That means, of course, that there is warming that will take place, as Dr. Stone has already mentioned, to which we will have to adapt. But IPCC findings also show that the choice of emissions path over this century will ultimately determine the climate that our grandchildren experience at the end of this century.
IPCC has reported on a number of observed changes. It reports that a warming of the climate system is unequivocal, as is evident from observations of increases in global air temperature and ocean temperatures, widespread melting of ice and snow, and so on. The total temperature increase from the late 19th century to the beginning of the 21st century is about three-quarters of a degree.
There are many other aspects of the climate system that are changing, and changing in a sense that is consistent with the warming that is taking place. There are changes in wind patterns, in the hydrological cycle, including precipitation and some aspects of extremes, and so on.
We have a great deal of information about the causes of these changes, and the IPCC has been making increasingly strong assessments in that regard. Each of those assessments is very conservative relative to the science that was available at the time.
For the second assessment report, the assessment was that there were slightly better than even odds of a human influence on climate.
For the third assessment report, the assessment was that it was “likely”--a term that has a specific IPCC meaning, which is that it has at least two chances in three of being correct--that most of the observed warming during the past 50 years at that time was due to human influence on the climate system.
For the fourth assessment report, that assessment is now very likely, so there is less than one chance in ten of the statement being incorrect, and likely substantially fewer chances than one in ten that most of the warming over the past 50 years is due to human influence on the climate system.
Also, there are assessments of many other changes in the climate system that have similarly been quantified, including changes in extremes, ocean interior temperatures, sea level, glaciers, atmospheric circulation, wind patterns, precipitation extremes, and droughts.
Projections for the next few decades are continued warming at about two-tenths of a degree Centigrade per decade, with about one-tenth of a degree Centigrade per decade already built into the system--committed warming. If we manage to stabilize atmospheric compositions at today's level, the climate would continue to warm and sea level would continue to rise for long periods of time.
The IPCC shows that there are substantial impacts from this warming. Some sectors and regions may initially benefit from warming that is taking place, but ultimately almost everybody suffers impacts, with increasing severity in number. Some sectors and regions that are likely to be impacted--again, more than two chances out of three--are the tundra, boreal forest, and mountain regions; snow and ice biomes, with sea ice biomes involving seals, polar bears, and so on; water resources in dry regions; low-lying coastal systems; and so on.
There are many implications for Canada. We have observed in Canada a rise in average temperature of 1.2°C since 1950. That's about twice the global rate. Warming that has been observed in Canada is attributable to increasing concentrations of greenhouse gases. There have been changes in precipitation over this period. Stream flow in rivers flowing into the Arctic has increased. The hydrological regime on many river systems has changed, with earlier peak flows and changes in the magnitude of peak flows.
Projections indicate that there will be continued warming over Canada at roughly double the global rate, with amplified changes in the north and greater vulnerability to drought despite increased precipitation over our land mass. Water levels in the Great Lakes and in the St. Lawrence River are likely to decline. There will be a continued loss of sea ice, permafrost, snow cover, and so on.
Professor Stone discussed the mitigation pathways that were assessed in the IPCC, indicating that emissions should peak by 2050 and be reduced by 20% to 85% below year 2000 levels to limit warming to somewhere below 2.4°C, or in the range of 2°C to 2.4°C. The risk of exceeding 2.4°C is substantial nonetheless, because the IPCC assessments do not account for uncertainties due to climate sensitivity--the amount that climate responds to the release of a fixed amount of greenhouse gas--or carbon cycle feedbacks, the possibility that carbon that is currently stored in soils, in ecosystems, and in oceans may be released to the climate system as the climate system warms, further driving the climate system to additional warming.
This has been an area of very active research recently. This research indicates that the key determinant of future stabilized warming is the total amount of global emissions of carbon dioxide accumulated over time--that is, the total amount ever to be released from pre-industrial to the present and on into the future.
This research indicates that warming can likely--meaning a 66% probability or more--be kept below 2°C if the post-2000 cumulative emissions do not exceed a number of about 560 petagrams of carbon. We're currently emitting about 10 petagrams of carbon per year. At current rates, that means 59 years of emissions.
Warming can very likely--meaning with greater than 90% certainty--be kept below 2°C if post-2000 cumulative emissions do not exceed 170 petagrams of carbon. But note that we're already 44% along the road to using up that 90%, since 74 petagrams of carbon were emitted between 2001 and 2008, cumulative.
Emissions pathways that peak earlier may allow more gradual subsequent emissions reductions, although there is also research that indicates that the probability of exceeding 2°C increases if mid-21st century, or 2050, emission rates remain high.
A further uncertainty that needs to be taken into account is that as emissions are reduced, the cooling effects of aerosols that currently offset the warming of non-CO2 greenhouse gases begin to diminish, and therefore the effects of those non-CO2 greenhouse gases start to become more apparent.
Ultimately, the degree of risk that is tolerable is a societal choice. It's not one that scientists can inform. We can only help to provide the factual information with which you will make those decisions.
So it's a societal choice as to whether we want to risk a warming in excess of 2°C at a level of 66%, a one-third chance of exceeding that level of warming, or a level with greater certainty, allowing ourselves perhaps only one chance in ten of exceeding that level. If the choice is to take a conservative approach and to minimize the risk, then we need to begin to curtail emissions very rapidly on a global scale.