5.8 Key conclusions and their uncertainties, confidence levels and research gaps
5.8.1 Findings and key conclusions
Projected changes in the frequency and severity of extreme climate events will have more serious consequences for food and forestry production, and food insecurity, than will changes in projected means of temperature and precipitation (high confidence).
Modelling studies suggest that increasing frequency of crop loss due to extreme events, such as droughts and heavy precipitation, may overcome positive effects of moderate temperature increase [5.4.1]. For forests, elevated risks of fires, insect outbreaks, wind damage and other forest-disturbance events are projected, although little is known about their overall effect on timber production [5.4.1].
Climate change increases the number of people at risk of hunger (high confidence). The impact of chosen socio-economic pathways (SRES scenario) on the numbers of people at risk of hunger is significantly greater than the impact of climate change. Climate change will further shift the focus of food insecurity to sub-Saharan Africa.
Climate change alone is estimated to increase the number of undernourished people to between 40 million and 170 million. By contrast, the impacts of socio-economic development paths (SRES) can amount to several hundred million people at risk of hunger [5.6.5]. Moreover, climate change is likely to further shift the regional focus of food insecurity to sub-Saharan Africa. By 2080, about 75% of all people at risk of hunger are estimated to live in this region. The effects of climate mitigation measures are likely to remain relatively small in the early decades; significant benefits of mitigation to the agricultural sector may be realised only in the second half of this century, i.e., once the positive CO2 effects on crop yields level off and global mean temperature increases become significantly less than in non-mitigated scenarios [5.6.5].
While moderate warming benefits crop and pasture yields in mid- to high-latitude regions, even slight warming decreases yields in seasonally dry and low-latitude regions (medium confidence).
The preponderance of evidence from models suggests that moderate local increases in temperature (to 3ºC) can have small beneficial impacts on major rain-fed crops (maize, wheat, rice) and pastures in mid- to high-latitude regions, but even slight warming in seasonally dry and tropical regions reduces yield. Further warming has increasingly negative impacts in all regions [5.4.2 and see Figure 5.2]. These results, on the whole, project the potential for global food production to increase with increases in local average temperature over a range of 1 to 3ºC, but above this range to decrease [5.4, 5.6]. Furthermore, modelling studies that include extremes in addition to changes in mean climate show lower crop yields than for changes in means alone, strengthening similar TAR conclusions [5.4.1]. A change in frequency of extreme events is likely to disproportionately impact small-holder farmers and artisan fishers [5.4.7].
Experimental research on crop response to elevated CO2 confirms Third Assessment Report (TAR) findings (medium to high confidence). New Free-Air Carbon Dioxide Enrichment (FACE) results suggest lower responses for forests (medium confidence). Crop models include CO2 estimates close to the upper range of new research (high confidence), while forest models may overestimate CO2 effects (medium confidence).
Recent results from meta-analyses of FACE studies of CO2 fertilisation confirm conclusions from the TAR that crop yields at CO2 levels of 550 ppm increase by an average of 15%. Crop model estimates of CO2 fertilisation are in the range of FACE results [5.4.1.1]. For forests, FACE experiments suggest an average growth increase of 23% for younger tree stands, but little stem-growth enhancement for mature trees. The models often assume higher growth stimulation than FACE, up to 35% [5.4.1.1, 5.4.5].
Globally, commercial timber productivity rises modestly with climate change in the short and medium term, with large regional variability around the global trend (medium confidence).
Overall, global forest products output at 2020 and 2050 changes, ranging from a modest increase to a slight decrease depending on the assumed impact of CO2 fertilisation and the effect of disturbance processes not well represented in the models (e.g., insect outbreaks), although regional and local changes will be large [5.4.5.2].
Local extinctions of particular fish species are expected at edges of ranges (high confidence).
Regional changes in the distribution and productivity of particular fish species are expected because of continued warming and local extinctions will occur at the edges of ranges, particularly in freshwater and diadromous species (e.g., salmon, sturgeon). In some cases, ranges and productivity will increase [5.4.6]. Emerging evidence suggests concern that the Meridional Overturning Circulation is slowing down, with serious potential consequences for fisheries [5.4.6].
Food and forestry trade is projected to increase in response to climate change, with increased dependence of most developing countries on food imports (medium to low confidence).
While the purchasing power for food is reinforced in the period to 2050 by declining real prices, it would be adversely affected by higher real prices for food from 2050 to 2080 [5.6.1, 5.6.2]. Food security is already challenged in many of the regions expected to suffer more severe yield declines. Agricultural and forestry trade flows are foreseen to rise significantly. Exports of food products from the mid and high latitudes to low latitude countries will rise [5.6.2], while the reverse may take place in forestry [5.4.5].
Simulations suggest rising relative benefits of adaptation with low to moderate warming (medium confidence), although adaptation may stress water and environmental resources as warming increases (low confidence).
There are multiple adaptation options that imply different costs, ranging from changing practices in place to changing locations of food, fibre, forestry and fishery (FFFF) activities [5.5.1]. The potential effectiveness of the adaptations varies from only marginally reducing negative impacts to, in some cases, changing a negative impact into a positive impact. On average in cereal cropping systems adaptations such as changing varieties and planting times enable avoidance of a 10-15% reduction in yield. The benefits of adaptation tend to increase with the degree of climate change up to a point [Figure 5.2]. Pressure to cultivate marginal land or to adopt unsustainable cultivation practices as yields drop may increase land degradation and endanger biodiversity of both wild and domestic species. Climate changes increase irrigation demand in the majority of world regions due to a combination of decreased rainfall and increased evaporation arising from increased temperatures, which, combined with expected reduced water availability, adds another challenge to future water and food security [5.9].
Summary of Impacts and Adaptive Results by Temperature and Time. Major generalisations across the FFFF sectors distilled from the literature are reported either by increments of temperature increase (Table 5.7) or by increments of time (Table 5.8), depending on how the information is originally reported. A global map of regional impacts of FFFF is shown in Figure 5.4.
Table 5.7. Summary of selected conclusions for food, fibre, forestry, and fisheries, by warming increments.
| Temp. Change | Sub-sector | Region | Finding | Source section |
|---|
| +1 to +2°C | Food crops | Mid- to high-latitudes | - Cold limitation alleviated for all crops - Adaptation of maize and wheat increases yield 10-15%; rice yield no change; regional variation is high | Figure 5.2 |
| | Pastures and livestock | Temperate | - Cold limitation alleviated for pastures; seasonal increased frequency of heat stress for livestock | Table 5.3 |
| | Food crops | Low latitudes | - Wheat and maize yields reduced below baseline levels; rice is unchanged - Adaptation of maize, wheat, rice maintains yields at current levels | Figure 5.2 |
| | Pastures and livestock | Semi-arid | - No increase in NPP; seasonal increased frequency of heat stress for livestock | Table 5.3 |
| | Prices | Global | - Agricultural prices: –10 to –30% | Figure 5.3 |
| +2 to +3°C | Food crops | Global | - 550 ppm CO2 (approx. equal to +2°C) increases C3 crop yield by 17%; this increase is offset by temperature increase of 2°C assuming no adaptation and 3°C with adaptation | Figure 5.2 |
| | Prices | Global | - Agricultural prices: –10 to +20% | Figure 5.3 |
| | Food crops | Mid- to high-latitudes | - Adaptation increases all crops above baseline yield | Figure 5.2 |
| | Fisheries | Temperate | - Positive effect on trout in winter, negative in summer | 5.4.6.1 |
| | Pastures and livestock | Temperate | - Moderate production loss in swine and confined cattle | Table 5.3 |
| | Fibre | Temperate | - Yields decrease by 9% | 5.4.4 |
| | Pastures and livestock | Semi-arid | - Reduction in animal weight and pasture production, and increased heat stress for livestock | Table 5.3 |
| | Food crops | Low latitudes | - Adaptation maintains yields of all crops above baseline; yields drops below baseline for all crops without adaptation | Figure 5.2 |
| +3 to +5°C | Prices and trade | Global | - Reversal of downward trend in wood prices - Agricultural prices: +10 to +40% - Cereal imports of developing countries to increase by 10-40% | 5.4.5.1 Figure 5.3 5.6.3 |
| | Forestry | Temperate | - Increase in fire hazard and insect damage | 5.4.5.3 |
| | | Tropical | - Massive Amazonian deforestation possible | 5.4.5 |
| | Food crops | Low latitudes | - Adaptation maintains yields of all crops above baseline; yield drops below baseline for all crops without adaptation | Figure 5.2 |
| | Pastures and livestock | Tropical | - Strong production loss in swine and confined cattle | Table 5.3 |
| | Food crops | Low latitudes | - Maize and wheat yields reduced below baseline regardless of adaptation, but adaptation maintains rice yield at baseline levels | Figure 5.2 |
| | Pastures and livestock | Semi-arid | - Reduction in animal weight and pasture growth; increased animal heat stress and mortality | Table 5.3 |
Table 5.8. Summary of selected findings for food, fibre, forestry and fisheries, by time increment.
| Time slice | Sub-sector | Location | Finding | Source |
|---|
| 2020 | Food crops | USA | - Extreme events, e.g., increased heavy precipitation, cause crop losses to US$3 billion by 2030 with respect to current levels | 5.4.2 |
| | Small-holder farming, fishing | Low latitudes, especially east and south Africa | - Decline in maize yields, increased risk of crop failure, high livestock mortality | 5.4.7 |
| | Small-holder farming, fishing | Low latitudes, especially south Asia | - Early snow melt causing spring flooding and summer irrigation shortage | 5.4.7 |
| | Forestry | Global | - Increased export of timber from temperate to tropical countries - Increase in share of timber production from plantations - Timber production +5 to +15% | 5.4.5.2 Table 5.4 |
| 2050 | Fisheries | Global | - Marine primary production +0.7 to +8.1%, with large regional variation (see Chapter 4) | 5.4.6.2 |
| | Food crops | Global | - With adaptation, yields of wheat, rice, maize above baseline levels in mid- to high-latitude regions and at baseline levels in low latitudes. | Figure 5.2 |
| | Forestry | Global | - Timber production +20 to +40% | Table 5.4 |
| 2080 | Food crops | Global | - Crop irrigation water requirement increases 5-20%, with range due to significant regional variation | 5.4.2 |
| | Forestry | Global | - Timber production +20 to +60% with high regional variation | Table 5.4 |
| | Agriculture sector | Global | - Stabilisation at 550 ppm ameliorates 70-100% of agricultural cost caused by unabated climate change | 5.4.2 |