IPCC:AR6/SRCCL/Chapter-2 - Revision history

Laura: /* CCB4 Climate change and urbanisation */

2026-05-31T07:13:50Z

CCB4 Climate change and urbanisation

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	Climate change is already affecting the health and energy demand of large numbers of people living in urban areas (''high confidence'') (Section 2.2). Future changes to both climate and urbanisation will enhance warming in cities and their surroundings, especially during heatwaves (''high confidence''). Urban and peri-urban agriculture and, more generally, the implementation of urban green infrastructure, can contribute to climate change mitigation (''medium confidence'') as well as to adaptation (''high confidence''), including co-benefits for food security and reduced soil-water-air pollution.		Climate change is already affecting the health and energy demand of large numbers of people living in urban areas (''high confidence'') (Section 2.2). Future changes to both climate and urbanisation will enhance warming in cities and their surroundings, especially during heatwaves (''high confidence''). Urban and peri-urban agriculture and, more generally, the implementation of urban green infrastructure, can contribute to climate change mitigation (''medium confidence'') as well as to adaptation (''high confidence''), including co-benefits for food security and reduced soil-water-air pollution.
			</div>
			<span id="climate-consequences-of-response-options"></span>

	~~<span id="climate-consequences-of-response-options"></span>~~
	== 2.6 Climate consequences of response options ==		== 2.6 Climate consequences of response options ==

Laura: /* 2.5.4 Non-local and downwind effects resulting from changes in land cover */

2026-05-31T07:13:03Z

2.5.4 Non-local and downwind effects resulting from changes in land cover

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	<span id="ccb4-climate-change-and-urbanisation"></span>		<span id="ccb4-climate-change-and-urbanisation"></span>
			<div class="container-box col-cross">

	== CCB4 Climate change and urbanisation ==		== CCB4 Climate change and urbanisation ==

Laura: /* 2.5.2.1 Impacts of deforestation and forestation */

2026-05-31T07:12:22Z

2.5.2.1 Impacts of deforestation and forestation

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	Deforestation or forestation<sup>[[#fn:2\|2]]</sup>, wherever it occurs, triggers simultaneously warming and cooling of the surface and of the atmosphere via changes in its various characteristics (Pitman 2003<sup>[[#fn:r1076\|1076]]</sup>; Strengers et al. 2010<sup>[[#fn:r1077\|1077]]</sup>; Bonan 2008<sup>[[#fn:r1078\|1078]]</sup>). Following deforestation, warming results from (i) the release of CO <sub>2</sub> and other GHGs in the atmosphere (biogeochemical impact) and subsequent increase in incoming infrared radiation at surface (greenhouse effect), (ii) a decrease in the total loss of energy through turbulent fluxes (latent and sensible heat fluxes) resulting from reduced surface roughness, (iii) an increased incoming solar radiation following reduced cloudiness that often (but not always) accompanies the decreased total evapotranspiration. Cooling occurs in response to (iv) increased surface albedo that reduces the amount of absorbed solar radiation, (v) reduced incoming infrared radiation triggered by the decreased evapotranspiration and subsequent decrease in atmospheric water vapour. Points ii–v are referred to as biophysical effects. Deforestation and forestation also alter rainfall and winds (horizontal as well as vertical, as will be further discussed below).		Deforestation or forestation<sup>[[#fn:2\|2]]</sup>, wherever it occurs, triggers simultaneously warming and cooling of the surface and of the atmosphere via changes in its various characteristics (Pitman 2003<sup>[[#fn:r1076\|1076]]</sup>; Strengers et al. 2010<sup>[[#fn:r1077\|1077]]</sup>; Bonan 2008<sup>[[#fn:r1078\|1078]]</sup>). Following deforestation, warming results from (i) the release of CO <sub>2</sub> and other GHGs in the atmosphere (biogeochemical impact) and subsequent increase in incoming infrared radiation at surface (greenhouse effect), (ii) a decrease in the total loss of energy through turbulent fluxes (latent and sensible heat fluxes) resulting from reduced surface roughness, (iii) an increased incoming solar radiation following reduced cloudiness that often (but not always) accompanies the decreased total evapotranspiration. Cooling occurs in response to (iv) increased surface albedo that reduces the amount of absorbed solar radiation, (v) reduced incoming infrared radiation triggered by the decreased evapotranspiration and subsequent decrease in atmospheric water vapour. Points ii–v are referred to as biophysical effects. Deforestation and forestation also alter rainfall and winds (horizontal as well as vertical, as will be further discussed below).

	The literature that discusses the effects of forestation on climate is more limited than for deforestation, but they reveal a similar climatic response with opposite sign, as further discussed below. For each latitudinal band (tropical, temperate and boreal) we look at how very large-scale deforestation or forestation impacts on the global mean climate, followed by an examination of the large-scale changes in the specific latitudinal band, and finally more regionally focused analysis. Large-scale idealised deforestation or forestation experiments are often carried out with global or regional climate models as they allow us to understand and measure how sensitive climate is to very large changes		The literature that discusses the effects of forestation on climate is more limited than for deforestation, but they reveal a similar climatic response with opposite sign, as further discussed below. For each latitudinal band (tropical, temperate and boreal) we look at how very large-scale deforestation or forestation impacts on the global mean climate, followed by an examination of the large-scale changes in the specific latitudinal band, and finally more regionally focused analysis. Large-scale idealised deforestation or forestation experiments are often carried out with global or regional climate models as they allow us to understand and measure how sensitive climate is to very large changes in land cover (similar to the instant doubling of CO <sub>2</sub> in climate models to calculate the climatic sensitivity to GHGs). Details of the model-based studies discussed below can be found in Table A2.2 in the Appendix.

	in land cover (similar to the instant doubling of CO <sub>2</sub> in climate models to calculate the climatic sensitivity to GHGs). Details of the model-based studies discussed below can be found in Table A2.2 in the Appendix.

	''Global and regional impacts of deforestation/forestation in tropical regions''		''Global and regional impacts of deforestation/forestation in tropical regions''
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	<span id="impacts-of-changes-in-land-management"></span>		<span id="impacts-of-changes-in-land-management"></span>

	==== 2.5.2.2 Impacts of changes in land management ====		==== 2.5.2.2 Impacts of changes in land management ====

Laura: /* 2.5.1.2 Impacts of future global land cover changes on climate */

2026-05-31T07:12:02Z

2.5.1.2 Impacts of future global land cover changes on climate

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	<span id="change-in-mean-global-annual-surface-air-temperature-resulting-from-anthropogenic-land-cover-changes-projected-for-the-future-according-to-three-different-scenarios-rcp8.5-rcp4.5-and-rcp2.6."></span>		<span id="change-in-mean-global-annual-surface-air-temperature-resulting-from-anthropogenic-land-cover-changes-projected-for-the-future-according-to-three-different-scenarios-rcp8.5-rcp4.5-and-rcp2.6."></span>

	<!-- IMG CAPTION -->		<!-- IMG CAPTION -->
	'''Change in mean global annual surface air temperature resulting from anthropogenic land cover changes projected for the future, according to three different scenarios: RCP8.5, RCP4.5 and RCP2.6.'''		'''Change in mean global annual surface air temperature resulting from anthropogenic land cover changes projected for the future, according to three different scenarios: RCP8.5, RCP4.5 and RCP2.6.'''

	Temperature changes resulting from biophysical and biogeochemical effects of land cover change are examined.		Temperature changes resulting from biophysical and biogeochemical effects of land cover change are examined.

	<!-- IMG FILE -->		<!-- IMG FILE -->
	[[File:06f33ed15db05e99f31259a8e97d2ea1 table-2.5.png]]		[[File:06f33ed15db05e99f31259a8e97d2ea1 table-2.5.png]]
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	<!-- END IMG -->		<!-- END IMG -->
	<span id="impacts-of-specific-land-use-changes"></span>		<span id="impacts-of-specific-land-use-changes"></span>

	=== 2.5.2 Impacts of specific land use changes ===		=== 2.5.2 Impacts of specific land use changes ===

Laura: /* 2.5.1.1 Impacts of global historical land cover changes on climate */

2026-05-31T07:10:52Z

2.5.1.1 Impacts of global historical land cover changes on climate

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	{\| class="wikitable"		{\| class="wikitable"
	\|-		\|-
			! Reference of the study
	Reference of the study		! Time period
			! Mean global annual change in surface air temperature (°C)
	Time period

	Mean global annual change in surface air temperature (°C)

	\|-		\|-
			\| Simmons and Matthews (2016)
	Simmons and Matthews (2016)		\| 1750–2000
			\| –0.02
	1750–2000

	–0.02

	\|-		\|-
			\| Shevliakova et al. (2013)
	Shevliakova et al. (2013)		\| 1861–2005
			\| +0.17
	1861–2005

	+0.17

	\|-		\|-
			\| Pongratz et al. (2010)
	Pongratz et al. (2010)		\| 1900–2000
			\| +0.14
	1900–2000

	+0.14

	\|-		\|-
			\| Matthews et al. (2004)
	Matthews et al. (2004)		\| 1700–2000
			\| +0.15
	1700–2000

	+0.15

	\|-		\|-
			\| Brovkin et al. (2004)
	Brovkin et al. (2004)		\| 1850–2000
			\| –0.05
	1850–2000

	–0.05

	\|-		\|-
			\| colspan="2" \| Mean ± standard deviation
	Mean ± standard deviation		\| 0.078 ± 0.093

	0.078 ± 0.093

	\|}		\|}
	<!-- END TABLE -->		<!-- END TABLE -->
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	<span id="impacts-of-future-global-land-cover-changes-on-climate"></span>		<span id="impacts-of-future-global-land-cover-changes-on-climate"></span>

	==== 2.5.1.2 Impacts of future global land cover changes on climate ====		==== 2.5.1.2 Impacts of future global land cover changes on climate ====

Laura: /* B 2.3 CO 2 fertilisation and enhanced terrestrial uptake of carbon */

2026-05-31T07:08:25Z

B 2.3 CO 2 fertilisation and enhanced terrestrial uptake of carbon

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	In summary, there is ''low confidence'' about the magnitude of the CO <sub>2</sub> effect and other factors that may explain at least a portion of the land sink (e.g., nitrogen deposition, increased growing season, reduced burning, erosion and re-deposition or organic sediments, aerosol-induced cooling). Increases in atmospheric CO <sub>2</sub> result in increased water use efficiency and increase leaf-level photosynthesis (''high confidence''). The extent to which CO <sub>2</sub> fertilisation results in plant- or ecosystem-level carbon accumulation is highly variable and affected by other environmental constraints (''high confidence''). Even in ecosystems where CO <sub>2</sub> fertilisation has been detected in recent decades, those effects are found to weaken as a result of physiological acclimation, soil nutrient limitation and other constraints on growth (Friend et al., 2014<sup>[[#fn:r790\|790]]</sup>; Körner, 2006<sup>[[#fn:r791\|791]]</sup>; Peñuelas et al., 2017<sup>[[#fn:r792\|792]]</sup>).		In summary, there is ''low confidence'' about the magnitude of the CO <sub>2</sub> effect and other factors that may explain at least a portion of the land sink (e.g., nitrogen deposition, increased growing season, reduced burning, erosion and re-deposition or organic sediments, aerosol-induced cooling). Increases in atmospheric CO <sub>2</sub> result in increased water use efficiency and increase leaf-level photosynthesis (''high confidence''). The extent to which CO <sub>2</sub> fertilisation results in plant- or ecosystem-level carbon accumulation is highly variable and affected by other environmental constraints (''high confidence''). Even in ecosystems where CO <sub>2</sub> fertilisation has been detected in recent decades, those effects are found to weaken as a result of physiological acclimation, soil nutrient limitation and other constraints on growth (Friend et al., 2014<sup>[[#fn:r790\|790]]</sup>; Körner, 2006<sup>[[#fn:r791\|791]]</sup>; Peñuelas et al., 2017<sup>[[#fn:r792\|792]]</sup>).
			</div>
			<span id="emissions-and-impacts-of-short-lived-climate-forcers-slcf-from-land"></span>

	~~<span id="emissions-and-impacts-of-short-lived-climate-forcers-slcf-from-land"></span>~~
	== 2.4 Emissions and impacts of short-lived climate forcers (SLCF) from land ==		== 2.4 Emissions and impacts of short-lived climate forcers (SLCF) from land ==

Laura: /* B2.2 Methodologies for estimating national to global scale anthropogenic land carbon fluxes */

2026-05-31T07:07:55Z

B2.2 Methodologies for estimating national to global scale anthropogenic land carbon fluxes

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	'''Country Reporting of GHG Inventories (GHGIs)''' : All parties to the UNFCCC are required to report national GHGIs of anthropogenic emissions and removals. Reporting requirements are differentiated between developed and developing countries. Because of the difficulty of separating direct anthropogenic fluxes from indirect or natural fluxes, the IPCC (2003)<sup>[[#fn:r735\|735]]</sup> adopted the ‘managed land’ concept as a proxy to facilitate GHGI reporting. All GHG fluxes on ‘managed land’ are defined as anthropogenic, with each country applying their own definition of ‘managed land’ (i.e., ‘where human interventions and practices have been applied to perform production, ecological or social functions’ (IPCC 2006)<sup>[[#fn:r736\|736]]</sup>). Fluxes may be determined on the basis of changes in carbon stocks (e.g., from forest inventories) or by activity data (e.g., area of land cover change management activity multiplied by emission factors or with modelled fluxes). Depending on the specific methods used, GHGIs include all direct anthropogenic effects and may include the indirect anthropogenic effects of environmental change (generally sinks) and natural effects (Section 2.3.1.2). GHG fluxes from ‘unmanaged land’ are not reported in GHGIs because they are assumed to be non-anthropogenic. The reported estimates may then be filtered through agreed ‘accounting rules’ (i.e., what countries actually count towards their mitigation targets (Cowie et al. 2007<sup>[[#fn:r737\|737]]</sup>; Lee and Sanz 2017<sup>[[#fn:r738\|738]]</sup>). The accounting aims to better quantify the additional mitigation actions by, for example, factoring out the impact of natural disturbances and forest age-related dynamics (Canadell et al. 2007<sup>[[#fn:r739\|739]]</sup>; Grassi et al. 2018<sup>[[#fn:r740\|740]]</sup>).		'''Country Reporting of GHG Inventories (GHGIs)''' : All parties to the UNFCCC are required to report national GHGIs of anthropogenic emissions and removals. Reporting requirements are differentiated between developed and developing countries. Because of the difficulty of separating direct anthropogenic fluxes from indirect or natural fluxes, the IPCC (2003)<sup>[[#fn:r735\|735]]</sup> adopted the ‘managed land’ concept as a proxy to facilitate GHGI reporting. All GHG fluxes on ‘managed land’ are defined as anthropogenic, with each country applying their own definition of ‘managed land’ (i.e., ‘where human interventions and practices have been applied to perform production, ecological or social functions’ (IPCC 2006)<sup>[[#fn:r736\|736]]</sup>). Fluxes may be determined on the basis of changes in carbon stocks (e.g., from forest inventories) or by activity data (e.g., area of land cover change management activity multiplied by emission factors or with modelled fluxes). Depending on the specific methods used, GHGIs include all direct anthropogenic effects and may include the indirect anthropogenic effects of environmental change (generally sinks) and natural effects (Section 2.3.1.2). GHG fluxes from ‘unmanaged land’ are not reported in GHGIs because they are assumed to be non-anthropogenic. The reported estimates may then be filtered through agreed ‘accounting rules’ (i.e., what countries actually count towards their mitigation targets (Cowie et al. 2007<sup>[[#fn:r737\|737]]</sup>; Lee and Sanz 2017<sup>[[#fn:r738\|738]]</sup>). The accounting aims to better quantify the additional mitigation actions by, for example, factoring out the impact of natural disturbances and forest age-related dynamics (Canadell et al. 2007<sup>[[#fn:r739\|739]]</sup>; Grassi et al. 2018<sup>[[#fn:r740\|740]]</sup>).
			</div>
	<div id="section-2-3-3-2-land-use-effects-block-3" class="box"></div>		<div id="section-2-3-3-2-land-use-effects-block-3" class="box"></div>

	<span id="b-2.3-co-2-fertilisation-and-enhanced-terrestrial-uptake-of-carbon"></span>		<span id="b-2.3-co-2-fertilisation-and-enhanced-terrestrial-uptake-of-carbon"></span>
			<div class="container-box col-regular">

	== B 2.3 CO <sub>2</sub> fertilisation and enhanced terrestrial uptake of carbon ==		== B 2.3 CO <sub>2</sub> fertilisation and enhanced terrestrial uptake of carbon ==

Laura: /* 2.3.3.2 Land use effects */

2026-05-31T07:07:10Z

2.3.3.2 Land use effects

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	<span id="b2.2-methodologies-for-estimating-national-to-global-scale-anthropogenic-land-carbon-fluxes"></span>		<span id="b2.2-methodologies-for-estimating-national-to-global-scale-anthropogenic-land-carbon-fluxes"></span>
			<div class="container-box col-regular">

	== B2.2 Methodologies for estimating national to global scale anthropogenic land carbon fluxes ==		== B2.2 Methodologies for estimating national to global scale anthropogenic land carbon fluxes ==

Laura: /* 2.3.1.2 Separation of the total net land flux into AFOLU fluxes and the land sink */

2026-05-31T07:05:17Z

2.3.1.2 Separation of the total net land flux into AFOLU fluxes and the land sink

Show changes

Laura: /* CCB3 Fire and climate change */

2026-05-31T06:42:05Z

CCB3 Fire and climate change

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	In summary, climate change is playing an increasing role in determining wildfire regimes alongside human activity (''medium confidence''), with future climate variability expected to enhance the risk and severity of wildfires in many biomes, such as tropical rainforests (''high confidence''). Fire weather seasons have lengthened globally between 1979 and 2013 (''low confidence''). Global land area burned has declined in recent decades, mainly due to less burning in grasslands and savannas (''high confidence''). While drought remains the dominant driver of fire emissions, there has recently been increased fire activity in some tropical and temperate regions during normal to wetter-than-average years due to warmer temperatures that increase vegetation flammability (''medium confidence''). The boreal zone is also experiencing larger and more frequent fires, and this may increase under a warmer climate (''medium confidence'').		In summary, climate change is playing an increasing role in determining wildfire regimes alongside human activity (''medium confidence''), with future climate variability expected to enhance the risk and severity of wildfires in many biomes, such as tropical rainforests (''high confidence''). Fire weather seasons have lengthened globally between 1979 and 2013 (''low confidence''). Global land area burned has declined in recent decades, mainly due to less burning in grasslands and savannas (''high confidence''). While drought remains the dominant driver of fire emissions, there has recently been increased fire activity in some tropical and temperate regions during normal to wetter-than-average years due to warmer temperatures that increase vegetation flammability (''medium confidence''). The boreal zone is also experiencing larger and more frequent fires, and this may increase under a warmer climate (''medium confidence'').
			</div>
			<span id="greenhouse-gas-fluxes-between-land-and-atmosphere"></span>

	~~<span id="greenhouse-gas-fluxes-between-land-and-atmosphere"></span>~~
	== 2.3 Greenhouse gas fluxes between land and atmosphere ==		== 2.3 Greenhouse gas fluxes between land and atmosphere ==