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

Abstract

The goal of limiting global mean warming to well below 2°C, and possibly to 1.5°C, emerged in the Paris Agreement, motivated by the belief that achieving these targets 'would significantly reduce the risks and impacts of climate change'. Understanding the climate impacts of relatively low levels of warming, in particular whether there are substantial benefits to reducing emissions to limit warming to 1.5°C rather than 2°C, is important for informing climate policy, but such studies are scarce. Here we evaluate the difference in global biophysical and economic impacts related to agriculture between 1.5°C-2°C warming. Given the small difference in global average temperature, accounting for uncertainties is important, and we include key uncertainties in three main components of the analysis: climate system (regional climate variability), biophysical system (crop response to CO 2 fertilization), and economic system (trade responsiveness). We are unable to meaningfully distinguish the regional agricultural impacts occurring with 1.5°C warming from those occurring with 2°C warming when accounting for these uncertainties. Under some assumptions 1.5°C implies benefits relative to 2°C, while under others it implies costs. Results are most sensitive to the uncertainty in the effect of CO 2 fertilization on crop yield.

Using the anomaly forcing Community Land Model (CLM 4.5) for crop yield projections

“…The global 70-year averaged yields ± standard deviation in the standard CLM (Ren et al, 2018) and in the anomaly forcing CLM are 4.38 ± 0.09 and 4.03 ± 0.16 t/ha, respectively, in the 1.5 • C scenario; 4.36 ± 0.11 and Figure 2. 70-year averaged differences between anomaly forcing and regular forcing for rain (a-c) and snow (d-f) for the 1.5, 2.0 • C, and RCP4.5 scenarios.…”

“…For the crop yield analysis, we aggregated the individual crop yield into an integrated crop yield by area weighted mean based on the crop area map MAPSMAP (https://www.mapspam.info/, last access: 1 March 2021) 2005 crop area. The regional crop yield was simply the regional averaged crop yield at nine regions defined in Ren et al (2018).…”

“…Increasing numbers of future climate scenarios exhibit large uncertainties for crop yield projections. Crop yields may increase or decrease depending on which climate projection is used (Lobell et al, 2008;Rosenzweig et al, 2014;Urban et al, 2012). Ensemble future climate projections, such as CMIP5, showed a large range of future climate projections, even for one emission scenario (Knutti and Sedlacek, 2013).…”

Introductory Chapter: Addressing Past Claims and Oncoming Challenges for Irrigation Systems

“…However, agriculture is not only a contributor to climate change, it will also be severely affected by climate change [19]. Moreover, some effects of warming on crop yields, increased pest occurrences, and the effects of extreme events (e.g., floods, storms, and droughts) on agricultural production are already observed [20]. Although farmers have long adapted to environmental conditions, the severity of the predicted climate changes may be beyond many farmers' current ability to adapt and improve their agricultural production systems and livelihoods [21].…”

The Economics of 1.5°C Climate Change

“…Climate change is already affecting crop yields, with more negative impacts than positive ones, and with the positive impacts being predominantly at high latitudes (86). As the climate warms to 1.5 • C and 2 • C, the number of negative impacts is expected to rise, and to become predominant in most world regions, although positive effects could still be seen in some regions if CO 2 fertilization occurs (87,88). However, the CO 2 fertilization effect is very uncertain and may be offset by declines in the protein content of crops, or damage from tropospheric ozone (86).…”