In the last 3 posts, I’ve reported on three studies making climate projections for St. Louis or Columbia by Hayhoe, VanDorn, Naik, and Wuebbles (2009), by Posey (2014), and by Anderson, Gooden, Guinan, Knapp, McManus, and Shulski (2015).
Because there is uncertainty associated with all climate projections, and because that uncertainty is magnified when making projections at the local level, there is value in having multiple projections from multiple studies. It can help to reduce some sources of uncertainty, though it cannot eliminate the uncertainty, by any means.
However, it is not always common for different climate studies to replicate methods precisely. Differences in method affect the resulting projections, and it means that the projections from these three studies should only be compared with great care. Some of the methodological differences include studying slightly different regions, making projections for different time periods, and using different climate scenarios.
Perhaps a bit of an amplification on the climate scenarios is in order here. It is thought that changes in climate will be sensitive to how humans respond to climate change, especially how we change or don’t change our greenhouse gas emissions. Climate change is already occurring, and most climate scientists agree that it is going to cause negative effects, no matter what we do – it is already too late to prevent them entirely. If GHG emissions rise from current levels, however, climate change is expected to be more severe. If we significantly curtail GHG emissions, climate change is expected to be less severe. If we follow a middle path, climate change is expected to follow a middle path.
Both climate change itself and mitigating climate change are expected to have implications for a variety of socio-economic factors – economic growth, poverty, social justice, migration, etc. To try to take these factors into account, climate scientists developed what they called scenarios. Each scenario outlined a path the world could take that included GHG emissions and a variety of socio-economic factors.
Three scenarios, the A1fi, the A2, and the B1, were used to make climate projections by these authors. They are shown on Figure 1. This chart is now 16 years old, but it shows the original conceptualization. The lines depict the expected cumulative amount of carbon dioxide emissions projected to occur under various scenarios. The A1fi scenario was projected to result in the highest emissions in the group shown, though by no means the highest possible emissions. The A2 scenario was projected to have somewhat lower emissions, and the B1 lower still, though by no means the lowest possible.
(Click on chart or table for larger view.)
You don’t have to look at this chart for very long before you understand that, other things being equal, climate projections using the A1fi Scenario might be expected to result in larger changes in climate, while those using the A2 scenario might result in smaller changes, and those using the B1 scenario might result in smaller changes yet.
Table 1 summarizes some of the projections from the three studies I’ve been reporting on.
You can’t make direct comparisons between the studies, but some trends can be seen:
- All three studies project temperature to increase by mid-century. Those that made projections for the end of the century projected it to increase even more by then.
- The two studies that made projections for mid-century for each of two scenarios found that temperature would increase more under a higher emission scenario than a lower emission scenario.
- The two studies that made projections related to heat waves agreed that the number of very hot days would increase.
- All three studies projected that average annual precipitation would increase by a small amount.
- Four out of five projections were for decreased precipitation in summer, with an increase during other seasons of the year.
- All three studies projected an increase in the number of days with heavy rain. Both studies that projected the maximum amount of rain over multi-day periods projected an increase.
- Both studies that projected the number of frost-free days per year projected that they would increase.
Only in two areas were there significant disagreements between the studies. First, the season in which the greatest change in temperature would occur differed, with one study projecting summer, one spring, and one winter. Second, of the two studies that projected seasonal changes in precipitation under the low emission scenario, one predicted a summer decrease and one predicted a summer increase.
Temperature projections using the A1fi, A2, and B1 scenarios followed the trend that would be expected from GHG emissions under those scenarios: higher, middle, and lower. Projections were made for 30-year periods centered on 2035, 2050, 2065, and 2084. The temperature was projected to increase more with each passing period.
Thus, despite their methodological differences, there appears to be a good deal of consistency between the results of these studies. They point to a warmer, slightly wetter local climate, with an increased frequency of heavy rain events.
Anderson, Christopher, Jennifer Gooden, Patrick Guinan, Mary Knapp, Gary McManus, and Martha Shulski. 2015. Climate in the Heartland: Historical Data and Future Projections for the Heartland Regional Network. Downloaded 3/15/16 from http://www.marc.org/Government/GTI/pdf/ClimateintheHeartlandReport.aspx.
Hayhoe, K, J VanDorn, V. Naik, and D. Wuebbles. 2009. “Climate Change in the Midwest: Projections of Future Temperature and Precipitation.” Technical Report on Midwest Climate Impacts for the Union of Concerned Scientists. Downloaded from http://www.ucsusa.org/global_warming/science_and_impacts/impacts/climate-change-midwest.html#.VvK-OD-UmfA.
Intergovernmental Panel on Climate Change. 2000. IPCC Special Report: Emissions Scenarios: Summary for Policymakers. https://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf.
Posey, John. 2014. “Climate Change in St. Louis: Impacts and Adaptation Options.” International Journal of Climate Change: Impacts and Responses. Vol 5, #2. Downloaded 1/15/2016 from http://ijc.cgpublisher.com/product/pub.185/prod.233.