Changes in climate extremes, fresh water availability and vulnerability to food insecurity projected at 1.5°C and 2°C global warming with a higher-resolution global climate model

Abstract

We projected changes in weather extremes, hydrological impacts and vulnerability to food insecurity at global warming of 1.5°C and 2°C relative to pre-industrial, using a new global atmospheric general circulation model HadGEM3A-GA3.0 driven by patterns of sea-surface temperatures and sea ice from selected members of the 5th Coupled Model Intercomparison Project (CMIP5) ensemble, forced with the RCP8.5 concentration scenario. To provide more detailed representations of climate processes and impacts, the spatial resolution was N216 (approx. 60 km grid length in mid-latitudes), a higher resolution than the CMIP5 models. We used a set of impacts-relevant indices and a global land surface model to examine the projected changes in weather extremes and their implications for freshwater availability and vulnerability to food insecurity. Uncertainties in regional climate responses are assessed, examining ranges of outcomes in impacts to inform risk assessments. Despite some degree of inconsistency between components of the study due to the need to correct for systematic biases in some aspects, the outcomes from different ensemble members could be compared for several different indicators. The projections for weather extremes indices and biophysical impacts quantities support expectations that the magnitude of change is generally larger for 2°C global warming than 1.5°C. Hot extremes become even hotter, with increases being more intense than seen in CMIP5 projections. Precipitation-related extremes show more geographical variation with some increases and some decreases in both heavy precipitation and drought. There are substantial regional uncertainties in hydrological impacts at local scales due to different climate models producing different outcomes. Nevertheless, hydrological impacts generally point towards wetter conditions on average, with increased mean river flows, longer heavy rainfall events, particularly in South and East Asia with the most extreme projections suggesting more than a doubling of flows in the Ganges at 2°C global warming. Some areas are projected to experience shorter meteorological drought events and less severe low flows, although longer droughts and/or decreases in low flows are projected in many other areas, particularly southern Africa and South America. Flows in the Amazon are projected to decline by up to 25%. Increases in either heavy rainfall or drought events imply increased vulnerability to food insecurity, but if global warming is limited to 1.5°C, this vulnerability is projected to remain smaller than at 2°C global warming in approximately 76% of developing countries. At 2°C, four countries are projected to reach unprecedented levels of vulnerability to food insecurity.This article is part of the theme issue ‘The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels’.

Challenges, Opportunities, and Pitfalls for Global Coupled Hydrologic‐Hydraulic Modeling of Floods

“…However, it should be noted that similarly to the MDB, many other large catchments worldwide have a complex river network and experience large interannual and interdecadal hydrological variability associated with climate modes such as El Niño‐Southern Oscillation, Pacific Decadal Oscillation, and the North Atlantic Oscillation. Moreover, current climate change projection studies highlight a possible amplification of wet and dry extremes (e.g., Armal et al, ; Betts et al, ; Lu et al, ; Taye et al, ; Trenberth et al, ). Furthermore, the large impact of local morphologic features highlighted in this study alludes to the importance of accounting for the potential impact of flood defenses in flood inundation prediction models, although a complete and accessible database of such infrastructure is currently not available, except for a very limited number of countries or regions.…”

Predicted Chance That Global Warming Will Temporarily Exceed 1.5 °C

“…The Paris Agreement (UNFCCC, ) also recognizes “the importance of averting, minimizing and addressing loss and damage associated with the adverse effects of climate change, including extreme weather events ….” There is clear evidence that greater global mean warming increases the risk of extreme weather events (Seneviratne et al, ), impacting food security (Betts et al, ), temperature extremes, and hence mortality rates, in many regions including Europe (Dosio & Fischer, ; King & Karoly, ), Australia (King et al, ), China, and East Asia (Li et al, ; Shi et al, ), European storms and precipitation extremes (Barcikowska et al, ), and coral bleaching events in the Great Barrier Reef (King et al, ). Hence, even temporary excursions of global mean temperature above 1.5 °C, with associated increases in the risks of extreme weather events, are relevant for policy makers.…”

Economic and biophysical impacts on agriculture under 1.5 °C and 2 °C warming

“…Schleussner et al (2016) assessed multiple biophysical impacts, including regional crop yields, concluding that while results vary between regions and crop types, both scenarios could result in significant yield reduction. Betts et al (2018) evaluated differences in vulnerability to food security, finding that although most countries would be less vulnerable in 1.5°C scenario than with 2°C, 24% of the countries would have the same or higher vulnerability at 1.5°C. AgMIP (Agricultural Model Intercomparison and Improvement Project) has organized multi-model studies to assess impacts at these levels of warming in the context of climate, crop, and economic uncertainties (Rosenzweig et al 2018, Ruane et al 2018, Schleussner et al 2018.…”

“…These studies demonstrate that uncertainty is especially important to account for given the relatively small difference in global mean temperature between the two scenarios. It is possible that uncertainty in regional climate or biophysical or economic impact models could be large relative to the global mean climate difference (Betts et al 2018). Several previous studies have considered particular aspects of uncertainty in agricultural impacts, including uncertainty in climate projections (e.g.…”