Editing IPCC:AR6/SR15/Chapter-3 (section)

==== 3.5.5.10 Agricultural systems: livestock in the tropics and subtropics ====

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The potential impacts of climate change on livestock (Section 3.4.6), in particular the direct impacts through increased heat stress, have been less well studied than impacts on crop yield, especially from the perspective of critical thresholds being exceeded. A case study from Jamaica revealed that the difference in heat stress for livestock between 1.5°C and 2°C of warming is ''likely'' to exceed the limits for normal thermoregulation and result in persistent heat stress for these animals (Lallo et al., 2018) <sup>[[#fn:r1262|1262]]</sup> . It is plausible that this finding holds for livestock production in both tropical and subtropical regions more generally ( ''medium confidence'' ) (Section 3.4.6). Under 3°C of global warming, significant reductions in the areas suitable for livestock production could occur ( ''low confidence'' ), owing to strong increases in regional temperatures in the tropics and subtropics ( ''high confidence'' ) ''.'' Thus, regional tipping points in the viability of livestock production may well exist, but ''little evidence'' quantifying such changes exists.

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'''Table 3.7'''

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'''Summary of enhanced risks in the exceedance of regional tipping points under different global temperature goals'''

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{| class="wikitable"
|-
! Tipping point
! Warming of 1.5°C or less
! Warming of 1.5°C–2°C
! Warming of up to 3°C
|-
| Arctic sea ice
| Arctic summer sea ice is ''likely'' to be maintained
Sea ice changes reversible under suitable climate<br />
restoration

| The risk of an ice-free Arctic in summer is about 50% or higher
Sea ice changes reversible under suitable climate restoration

| Arctic is ''very likely'' to be ice free in summer
Sea ice changes reversible under suitable climate<br />
restoration

|-
| Tundra
| Decrease in number of growing degree days<br />
below 0°CAbrupt increases in tree cover are ''unlikely''
| Further decreases in number of growing degree days below 0°C
Abrupt increased in tree cover are ''unlikely''

| Potential for an abrupt increase in tree fraction<br />
( ''low confidence'' )
|-
| Permafrost
| 17–44% reduction in permafrost
Approximately 2 million km <sup>2</sup> more permafrost maintained than under 2°C of global warming ( ''medium confidence'' )

Irreversible loss of stored carbon

| 28–53% reduction in permafrost
Irreversible loss of stored carbon

| Potential for permafrost collapse ( ''low confidence'' )
|-
| Asian monsoon
| ''Low confidence'' in projected changes
| Increases in the intensity of monsoon precipitation ''likely''
|-
| West African monsoon and the Sahel
| Uncertain changes; ''unlikely'' that a tipping point is<br />
reached
| Uncertain changes; ''unlikely'' that tipping point is reached
| Strengthening of monsoon with wettening and greening of the Sahel and Sahara ( ''low confidence'' )
Negative associated impacts through increases in extreme temperature events

|-
| Rainforests
| Reduced biomass, deforestation and fire increases pose uncertain risks to forest dieback
| Larger biomass reductions than under 1.5°C of warming; deforestation and fire increases pose uncertain risk to forest dieback
| Reduced extent of tropical rainforest in Central America and large replacement of rainforest by savanna and grassland
Potential tipping point leading to pronounced forest dieback ( ''medium confidence'' )

|-
| Boreal forests
| Increased tree mortality at southern boundary of<br />
boreal forest ( ''medium confidence'' )
| Further increases in tree mortality at southern boundary of boreal forest ( ''medium confidence'' )
| Potential tipping point at 3°C–4°C for significant dieback of boreal forest ( ''low confidence'' )
|-
| Heatwaves, unprecedented heat and human health
| Substantial increase in occurrence of potentially<br />
deadly heatwaves ( ''likely'' )More than 350 million more people exposed to deadly heat by 2050 under a midrange population growth scenario ( ''likely'' )
| Substantial increase in potentially deadly<br />
heatwaves ( ''likely'' )Annual occurrence of heatwaves similar to the deadly 2015 heatwaves in India and Pakistan<br />
( ''medium confidence'' )
| Substantial increase in potentially deadly<br />
heatwaves ''very likely''
|-
| Agricultural systems: key staple crops
| Global maize crop reductions of about 10%
| Larger reductions in maize crop production than<br />
under 1.5°C of about 15%
| Drastic reductions in maize crop globally and in Africa (high confidence)
Potential tipping point for collapse of maize crop in some regions<br />
( ''low confidence'' )

|-
| Livestock in the tropics and subtropics
| Increased heat stress
| Onset of persistent heat stress ( ''medium confidence'' )
| Persistent heat stress ''likely''
|}
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