Editing IPCC:AR6/SRCCL/TS (section)

=== Implications of climate change, variability and extremes for land systems ===

'''It is certain that globally averaged land surface air temperature (LSAT) has risen faster than the global mean surface temperature (i.e., combined LSAT and sea surface temperature) from the preindustrial period (1850–1900) to the present day (1999–2018). According to the single longest and most extensive dataset, from 1850–1900 to 2006–2015 mean land surface air temperature has increased by 1.53°C (''very likely range ''from 1.38°C to 1.68°C) while global mean surface temperature has increased by 0.87°C (''likely range ''from 0.75°C to 0.99°C). For the 1881–2018 period, when four independently produced datasets exist, the LSAT increase was 1.41°C (1.31–1.51°C), where the range represents the spread in the datasets’ median estimates.''' Analyses of paleo records, historical observations, model simulations and underlying physical principles are all in agreement that LSATs are increasing at a higher rate than SST as a result of differences in evaporation, land–climate feedbacks and changes in the aerosol forcing over land (''very high confidence''). For the 2000–2016 period, the land-to-ocean warming ratio (about 1.6) is in close agreement between different observational records and the CMIP5 climate model simulations (the ''likely range ''of 1.54–1.81). {2.2.1}

'''Anthropogenic warming has resulted in shifts of climate zones, primarily as an increase in dry climates and decrease of polar climates (''high confidence''). Ongoing warming is projected to result in new, hot climates in tropical regions and to shift climate zones poleward in the mid- to high latitude and upward in regions of higher elevation (''high confidence'').''' Ecosystems in these regions will become increasingly exposed to temperature and rainfall extremes beyond the climate regimes they are currently adapted to (''high confidence''), which can alter their structure, composition and functioning. Additionally, high-latitude warming is projected to accelerate permafrost thawing and increase disturbance in boreal forests through abiotic (e.g., drought, fire) and biotic (e.g., pests, disease) agents (''high confidence''). {2.2.1, 2.2.2, 2.5.3}

'''Globally, greening trends (trends of increased photosynthetic activity in vegetation) have increased over the last 2–3 decades by 22–33%, particularly over China, India, many parts of Europe, central North America, southeast Brazil and southeast Australia (''high confidence'').''' This results from a combination of direct (i.e., land use and management, forest conservation and expansion) and indirect factors (i.e., CO<sub>2</sub> fertilisation, extended growing season, global warming, nitrogen deposition, increase of diffuse radiation) linked to human activities (''high confidence''). Browning trends (trends of decreasing photosynthetic activity) are projected in many regions where increases in drought and heatwaves are projected in a warmer climate. There is ''low confidence ''in the projections of global greening and browning trends. {2.2.4, Cross-Chapter Box 4 in Chapter 2}

<!-- START IMG -->
<!-- IMG FILE -->
[[File:FigureTS3???.jpg]]
<!-- IMG TITLE -->
'''Figure TS.3 | The structure and functioning of managed and unmanaged ecosystems that affect local, regional and global climate.''' Land surface characteristics such as albedo and emissivity determine the amount of solar and long-wave radiation absorbed by land and reﬂected or emitted to the atmosphere. Surface roughness inﬂuences turbulent exchanges of momentum, energy, water and biogeochemical tracers. Land ecosystems modulate the atmospheric composition through emissions and removals of many GHGs and precursors of SLCFs, including biogenic volatile organic compounds (BVOCs) and mineral dust. Atmospheric aerosols formed from these precursors affect regional climate by altering the amounts of precipitation and radiation reaching land surfaces through their role in clouds physics.
<!-- END IMG -->

'''The frequency and intensity of some extreme weather and climate events have increased as a consequence of global warming and will continue to increase under medium and high emission scenarios (''high confidence'').''' Recent heat-related events, for example, heatwaves, have been made more frequent or intense due to anthropogenic GHG emissions in most land regions and the frequency and intensity of drought has increased in Amazonia, north-eastern Brazil, the Mediterranean, Patagonia, most of Africa and north-eastern China (''medium confidence''). Heatwaves are projected to increase in frequency, intensity and duration in most parts of the world (''high confidence'') and drought frequency and intensity is projected to increase in some regions that are already drought prone, predominantly in the Mediterranean, central Europe, the southern Amazon and southern Africa (''medium confidence''). These changes will impact ecosystems, food security and land processes including GHG fluxes (''high confidence''). {2.2.5}

'''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 savannahs (''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''). {Cross-Chapter Box 4 in Chapter 2}