Today the Intergovernmental Panel on Climate Change, or IPCC, released its latest report on the physical science behind climate change. The IPCC is the world’s pre-eminent scientific body on climate change, and it has compiled the latest scientific findings since its last report in 2007.
Governments meeting today in Stockholm, Sweden approved the Summary for Policymakers. Here are a few headlines compiled from the report by The Nature Conservancy’s climate science and policy experts:
- Our understanding of complex earth-climate system interactions is becoming increasingly clear, and is largely validating previous projections of climate change impacts.
- There is very high certainty among scientists (95%) that human activities (such as burning fossil fuels) is contributing to climate change (similar to the level of certainty that smoking cigarettes may cause cancer).
- If we do not quickly take strong steps to reduce carbon pollution, we risk crossing thresholds of dangerous impacts on ecological and geophysical systems.
- Warming of the climate system is unequivocal, and many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.
- The oceans have been storing more than 90% of the energy accumulated between 1971 and 2010, buffering climate change impacts on humanity. The oceans are now showing signs of stress, with sea level rise, increased acidification and even warming of the deep sea, which will affect the ocean circulation system.
- There is high confidence that the contrast between wet and dry seasons will increase over most of the globe as temperatures increase.
Below Senior Climate Scientist Evan Girvetz discusses some of the scientific underpinnings of the report, and the increasingly accurate use of climate models, in more detail.
By Evan Girvetz
Six years have passed since the last global climate assessment report from the Intergovernmental Panel on Climate Change (IPCC) — a body that coordinates thousands of the world’s leading climate experts to review and assess the science to date (830 authors contributed to this report).
There has certainly been plenty of rhetoric about global warming over the past six years, but when it comes down to the science behind our understanding of the “physical basis for climate change,” one could ask: What have we actually learned?
First, we learned that the general patterns of temperature and precipitation change projected by the global climate models have not changed substantially since the last IPCC report in 2007. Even with improvements, refinements, finer scale data, and many additional climate models (there are now more than twice the number of models), the projected temperature and precipitation changes around the globe are strikingly similar to what they were more than a half decade ago.
What does this mean? It means the new climate models are corroborating the older ones, suggesting increased scientific consensus about how greenhouse gases are affecting the planet’s climate system, causing temperature and precipitation changes.
The maps below show projected precipitation change during June – August for 2081-2100 from both the new IPCC report (left map) and the previous IPCC report (right map). The maps are almost identical to one another. Similarly, the amount of temperature change projected from different levels of greenhouse gas emissions is almost identical to what it was in the last IPCC report.
IPCC AR4 Data (2007)—19 GCMs IPCC AR5 Data (2013)—30 GCMs
Change in June – August precipitation by 2081-2100 relative to 1986-2005 for the ensemble average of 30 General Circulation Models (GCMs) from the most recent IPCC AR5 report (2013, left) and 19 GCMs from the last IPCC Report (2007, right). (Source: Reto Knutti* and Jan Sedláˇcek, 2012, Nature Climate Change: http://www.nature.com/nclimate/journal/v3/n4/full/nclimate1716.html)
Second, greenhouse gas emissions have continued to increase at the rate of the highest modeled scenarios from the current IPCC and previous scientific assessment reports. One of the biggest questions has been: how much will our global society be able to cut greenhouse gas emissions? And will we be able to keep global temperature increase below 2° C (or 3.6 degrees Fahrenheit, which climate scientists have said allows a reasonable chance of avoiding the worst impacts of climate change)?
In theory staying below a 2° C increase is possible, but in reality, our current observed emissions (shown as black dots below) are at the high end of the emissions scenarios considered by the IPCC and have put us on the track to 4° C or even higher global temperature change. This is shown by the red line representing Representative Concentration Pathway (RCP) 8.5. In order to keep global temperature increase below the 2 ° C emissions “safe” target, we will need to follow the emissions pathway similar to the blue line—which we currently are not doing.
Can we stay below global warming of 2 degrees Celsisus?
It is conceivable to hold temperature change below 2 °C, but action must be taken immediately. To accomplish this, emissions must peak by 2020 and then reductions of ~3% are required each year in the medium term (next 5-50 years), with net negative emissions in the long-term. In reality, our emissions are not looking like they will peak by 2020, rather they are increasing at a rate of about 2.5 – 3% per year right in line with the red, high emissions scenario. This means that we as a society need to shift quickly to lower-carbon development pathways, or we will rapidly approach more dangerous levels of increasing temperatures.
Even if we stopped polluting tomorrow, we are committed to serious climate change impacts based solely on carbon released into the atmosphere to date. These findings underscore the importance of our ability as a society to rapidly prepare our communities and natural resources to become more resilient to these likely changes.
One silver lining to this report is the confirmation that we have good information to help us understand what the likely impacts of climate change will be in different places. Tools developed by The Nature Conservancy and partners, such as the Climate Wizard(http://ClimateWizard.org) and Coastal Resilience (http://CoastalResilience.org) can help communities and regions to plan for their response.
We have improved understanding of how changes are likely to play out on the ground through reduced crop yields, landslides, flooding, droughts, fires, coastal storm surge and other impacts to people and nature. And we are finding solutions that are helping us prepare for these impacts.
The bottom line is that this new report helps advance scientific consensus about climate change: the sobering conclusion is that we are pumping dangerous amounts of carbon pollution into our air and oceans – and we have a vanishingly small window of opportunity to turn the ship around.
It is imperative that governments, communities and businesses adopt smart strategies to manage these growing risks to our communities and economy. We need to bring carbon pollution down to safe levels – needed to return our climate system to balance. And we need to get ready for the storms that lie ahead if we continue on this course.
Evan Girvetz is Senior Climate Scientist for The Nature Conservancy
Featured photo by: Flickr user World Bank Photo Collection (Factory smokestacks and power transmission lines.) Used under a Creative Commons license.
Photo 2: Flicker user poepoe374 (Waves crash over a sea wall during a storm.) Used under a Creative Commons license.
Photo 3: Mark Godfrey (TNC) (A frog on parched soil during a Missouri drought.)
Trackback from your site.