Publications Library

Publishing in the Reviews of Geophysics, Westra et al (2014) summarize the current state of research in the analysis of future changes to the intensity, frequency and duration of extreme rainfall. Their literature review highlights the complicated relationship between short duration extreme rainfall and atmospheric temperature. In some locations, such extreme precipitation does not simply scale with the ability of the atmosphere to hold moisture (i.e. at the Clausius-Clapyron rate of 6 to 7% per °C). Instead, at these locations the general pattern is that such a relationship is found to hold up to about 12 °C, but between 12 and 24 °C extreme precipitation appears to increase more strongly with warming. This is partly due to an increase in convective rainfall. However, above about 24 °C, the pattern at these locations is one in which the response of precipitation to increasing temperature appears to be weaker, eventually reversing. This may be due to decreased moisture availability at these temperatures, though Westra et al. note that “the mechanism that causes these moisture deficits remains to be investigated.” The authors also find that anticipated changes in sub-daily precipitation associated with a warming climate will “significantly affect the magnitude and frequency of urban and rural flash floods.”

Compared to daily rainfall, Westra et al. find that sub-daily and sub-hourly rainfall are more sensitive to local surface temperatures. They also report that while sub-daily precipitation observations are too scarce to determine regional trends, geographic location will likely affect rates of change in daily precipitation extremes. In terms of making projections of future changes in these events, the authors find that, owing to the resolution of current global climate models, they are limited in their ability to simulate such precipitation events. In particular, the models are generally not run at sufficient resolution to accurately resolve the necessary convective processes, though some very high-resolution “convection permitting” regional climate models operate at a sufficient resolution to potentially be useful in projecting such extremes. One implication of these findings is that we cannot currently make credible projections of sub-daily rainfall events.

Two articles recently published in the peer-review literature seek to answer two related questions: What role could utilizing vegetation burning for energy, with methods to capture the carbon dioxide emitted, have in aggressive short-term climate mitigation in western North America? And, how might North American vegetation and its interactions with the climate change in the future?

Addressing the first question in Nature Climate Change, Sanchez et al. (2015) find that western North America could attain a carbon-negative power system by 2050 through strong deployment of renewable energy sources, including BioEnergy with Carbon Capture and Storage (BECCS), and fossil fuel reductions. Their results indicate that reductions of up to 145% from 1990s emissions are possible. They also find that the primary value of BECCS is not electricity production, but carbon sequestration, and note that BECCS can also be used to reduce emissions in the transportation and industrial sectors.

Publishing in the Journal of Geophysical Research: Atmospheres, Garnaud and Sushama (2015) examine the second question. In order to do this they downscale output from a global climate model using a regional climate model that can simulate vegetation dynamics. They find that the projected future increases to growing season length result in greater vegetation productivity and biomass, though this plateaus at the end of of the 21st century. Their projections also indicate an increase in the water-use efficiency of plants, but decreased plant productivity in the southeastern US over the 2071-2100 period. In addition, they find that accounting for vegetation feedbacks leads to increased warming in summer at higher latitudes and a reduction in summer warming at lower latitudes.

Recent research by P.A. O’Gorman (2014), in the journal Nature, uses an ensemble of global climate model (GCM) simulations to examine the projected changes in both mean snowfall and daily snowfall extremes in a high greenhouse-gas emissions scenario. He finds that, while both mean snowfall and extreme snowfall decrease as the climate warms due to the influence of greenhouse gasses, the reduction in daily snowfall extremes is smaller than the reduction in mean snowfall. O’Gorman suggests, based on a simple physical model, that this may be due to snowfall extremes occuring near an optimal temperature that is insensitive to climate change.

In a recent paper in the journal Nature Climate Change, Meehl, Teng and Arblaster (2014) examine individual global climate model runs from models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to see if any runs replicated the observed early-2000s hiatus in surface temperature warming. They found that those individual model runs that have Interdecadal Pacific Oscillation (IPO) values that matched with observed values successfully simulate the early 2000s hiatus. Using data available in the mid-1990s, they also apply a recently-developed climate prediction technique that uses modern global climate models (GCM), initialized with observations, to make so-called “decadal climate predictions” and find that both the negative phase of the IPO and the surface temperature hiatus could be predicted with this method, using only data that was available prior to the hiatus.

In a recent article published in the journal Nature, Kossin et al. (2014) use satellite data and reanalysis products to see if there has been a shift in the latitudes at which tropical storms reach their maximum intensity over the 1982-2012 period. The authors find that, globally, the latitudes of maximum intensity have shifted poleward, 53 kilometres per decade in the Northern Hemisphere and 62 kilometres per decade in the Southern Hemisphere. This trend of poleward migration is evident in all ocean basins, except the North Indian Ocean basin, in homogenized satellite and so-called “best track” data. Kossin and colleagues note that this migration is apparently linked to: (1) the absolute difference between wind speeds in the upper and lower troposphere and (2) potential intensity. These have both experienced changes that can be linked to the expansion of the tropics, which is thought to be due, in part, to anthropogenic causes.

A recent meta-analysis published in the journal Nature Climate Change, by Challinor et al. (2014) examines 1,722 crop model simulations, run using global climate model output under several emissions scenarios, to evaluate the potential effects of climate change and adaptation on crop yield. The authors find that, without adaptation, projected corn, rice and wheat production is reduced when areas experience 2.0 °C or more of local warming, with losses greater in the second half of the century due to larger changes in climate. Crop-level adaptations are projected to be able to increase yields by an average of 7-15% when compared to similar scenarios that do not utilize adaptation. Projections indicate that adaptation may be more successful for wheat and rice than for corn. Though less data is available on yield variability, Challinor et al. find that it is likely to increase.

This Science Brief covers two papers by in the journal Atmosphere-Ocean, on future ocean conditions for British Columbia’s continental shelf. Using an ocean circulation model for the shelf, the authors find that surface temperatures may increase by 0.5 to 2.0 °C, seasonal surface salinity may drop by up to 2 PSS in some areas, and that Haida Eddies will strengthen, as will the Vancouver Island Coastal Current and freshwater discharges into coastal waters.