Editing IPCC:AR6/WGI/Chapter-Atlas (section)

=== Atlas.7.1 Central America and the Caribbean ===

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==== Atlas.7.1.1 Key Features of the Regional Climate and Findings From Previous IPCC Assessments ====

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===== Atlas.7.1.1.1 Key Features of the Regional Climate =====

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The Central America and Caribbean region is assessed considering three reference regions Southern Central America (SCA), including the isthmus and the Yucatan Peninsula; Northern Central America (NCA), including Mexico (centre and north); and the Caribbean (CAR), including the Greater Antilles, the Lesser Antilles, the Bahamas and other small islands (see Figure Atlas.22); NCA is also covered in Section [[#Atlas.9|Atlas.9]] North America.

Precipitation in most of SCA is characterized by two maxima in June and September, an extended dry season from November to May, and a shorter relatively dry season between July and August known as the midsummer drought (MSD; Chapter 10; [[#Magaña--1999|Magaña et al., 1999]] ; [[#Perdigón-Morales--2018|Perdigón-Morales et al., 2018]] ). To some extent, precipitation seasonality is explained by the migration of the Inter-tropical Convergence Zone (ITCZ) ( [[#Taylor--2005|Taylor and Alfaro, 2005]] ). The climate of NCA is temperate to the north of the Tropic of Cancer, with a marked difference between winter and summer, modulated by the North American Monsoon (NAmerM, [[IPCC:Wg1:Chapter:Chapter-8#8.3.2.4.4|Section 8.3.2.4.4]] ). The CAR region has two main seasons, characterized by differences in temperature and precipitation. The wet or rainy season, with higher values of temperature and accumulated precipitation, occurs during the boreal summer and part of spring and autumn ( [[#Gouirand--2020|Gouirand et al., 2020]] ). The MSD is also present in the Greater Antilles and the Bahamas ( [[#Taylor--2005|Taylor and Alfaro, 2005]] ), influenced by the oscillations of the North Atlantic Subtropical High (NASH), interacting with the Pacific and Atlantic branches of the ITCZ and modulated by the Atlantic Warm Pool and the Caribbean low-level jet (CLLJ), while the Atlantic ITCZ is responsible for the unimodal rainfall cycle of the central and southern Lesser Antilles ( [[#Martinez--2019|Martinez et al., 2019]] ). The CLLJ is a persistent climatological feature of the low-level circulation in the Central Caribbean, with a characteristic semi-annual cycle with maxima in the summer (main) and winter (secondary) ( [[#Amador--1998|Amador, 1998]] ; [[#Magaña--1999|Magaña et al., 1999]] ; [[#Whyte--2008|Whyte et al., 2008]] ). Temporal variability is influenced by several large-scale atmospheric modes ( [[IPCC:Wg1:Chapter:Annex-iv|Annex IV]] and Table Atlas.1). A significant positive correlation between precipitation rates in CAR and the Atlantic Multi-decadal Variability (AMV) was found ( [[#Enfield--2001|Enfield et al., 2001]] ). A similar result was found in southern Mexico (north of SCA) in the MSD region (see case-study discussion in [[IPCC:Wg1:Chapter:Chapter-10#10.4.2.3|Section 10.4.2.3]] ; [[#Méndez--2010|Méndez and Magaña, 2010]] ; [[#Cavazos--2020|Cavazos et al., 2020]] ). On the other hand, ENSO favours wet conditions in NCA, but its effect is modulated by Pacific Decadal Variability (PDV; [[#Maldonado--2016|Maldonado et al., 2016]] ).

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[[File:e4b6c43bd9d1331ce8736254d0b7c03e IPCC_AR6_WGI_Atlas_Figure_22.png]]

'''Figure Atlas.22''' '''|''' '''Regional changes over land in annual mean surface air temperature and precipitation relative to the 1995–2014 baseline for the reference regions in Central America, the Caribbean and South America (warming since the 1850–1900 pre-industrial baseline is also provided as an offset).''' Barplots in the left panel of each region triplet show the median (dots) and 10th–90th percentile range (bars) across each model ensemble for annual mean temperature changes for four datasets (CMIP5 in intermediate colours; a subset of CMIP5 used to drive CORDEX in light colours; CORDEX overlying the CMIP5 subset with dashed bars; and CMIP6 in solid colours); the first six groups of bars represent the regional warming over two time periods (near-term 2021–2040 and long-term 2081–2100) for three scenarios (SSP1-2.6/RCP2.6, SSP2-4.5/RCP4.5 and SSP5-8.5/RCP8.5), and the remaining bars correspond to four global warming levels (GWL: 1.5°C, 2°C, 3°C and 4°C). The scatter diagrams of temperature against precipitation changes display the median (dots) and 10th–90th percentile ranges for the above four warming levels for December–January–February (DJF; middle panel) and June–July–August (JJA; right panel), respectively; for the CMIP5 subset only the percentile range of temperature is shown, and only for 3°C and 4°C GWLs. Changes are absolute for temperature (in °C) and relative (as %) for precipitation. See [[#Atlas.1.3|Atlas.1.3]] for more details on reference regions ( [[#Iturbide--2020|Iturbide et al., 2020]] ) and [[#Atlas.1.4|Atlas.1.4]] for details on model data selection and processing. The script used to generate this figure is available online ( [[#Iturbide--2021|Iturbide et al., 2021]] ) and similar results can be generated in the Interactive Atlas for flexibly defined seasonal periods. Further details on data sources and processing are available in the chapter data table (Table Atlas.SM.15).

One of the most prominent features of the regional climate is the incidence of tropical cyclones (TCs), which represent an important hazard for almost all the countries of the region between June and November. A detailed assessment is given in Chapter 11.

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===== Atlas.7.1.1.2 Findings From Previous IPCC Assessments =====

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According to AR5 ( [[#Christensen--2013|Christensen et al., 2013]] ), significant positive trends of temperature have been observed in Central America ( ''high confidence'' ), while significant precipitation trends are regionally dependent, especially during the summer. In addition, changes in climate variability and in extreme events have severely affected the region ( ''medium confidence'' ). A decrease in mean precipitation is projected in SCA and NCA. El Niño and La Niña teleconnections are projected to move eastwards in the future ( ''medium confidence'' ), while changes in their effects on other regions, including Central America and the Caribbean is uncertain ( ''medium confidence'' ). There is ''medium confidence'' in projections showing an increase in seasonal mean precipitation on the equatorial flank of the ITCZ affecting parts of Central America and the Caribbean.

In relation to the 1986–2005 baseline period, temperatures are ''very likely'' to increase by the end of the century, even for the RCP2.6 scenario, with changes of more than 5°C in some regions for the RCP8.5 scenario. Precipitation change is projected to vary between +10% and –25% ( ''medium confidence'' ) ( [[#Christensen--2013|Christensen et al., 2013]] ). The SR1.5 ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ) states there is a ''high agreement'' and ''robust evidence'' that at the 1.5°C global warming level the Caribbean region will experience a 0.5°C–1.5°C warming compared to the 1971–2000 baseline period, with greatest warming over larger land masses.

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==== Atlas.7.1.2 Assessment and Synthesis of Observations, Trends and Attribution ====

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Significant warming trends between 0.2°C and 0.3°C per decade have been observed in the three reference regions of Central America in the last 30 years (Planos Gutiérrez et al., 2012; P.D. [[#Jones--2016|Jones et al., 2016]] a; [[#Hidalgo--2017|Hidalgo et al., 2017]] ), with the largest increases in the North American Monsoon region ( ''high confidence'' ) (Figure Atlas.11 and the Interactive Atlas; [[#Cavazos--2020|Cavazos et al., 2020]] ). There is ''high confidence'' of increasing temperature over parts of NCA, reaching 0.5°C per decade in Mexico and southern Baja California, with a lower rate (0.2°C per decade) in the Yucatan Peninsula and the Guatemala Pacific coastal region ( [[#Cueto--2010|Cueto et al., 2010]] ; [[#García%20Cueto--2013|García Cueto et al., 2013]] ; [[#Martínez-Austria--2016|Martínez-Austria et al., 2016]] ; [[#Martínez-Austria--2017|Martínez-Austria and Bandala, 2017]] ; [[#Navarro-Estupiñan--2018|Navarro-Estupiñan et al., 2018]] ; [[#Cavazos--2020|Cavazos et al., 2020]] ) and CAR ( [[#McLean--2015|McLean et al., 2015]] ) over the last 30 to 40 years. Cooling trends have been detected in limited areas of Honduras and northern Panama ( [[#Hidalgo--2017|Hidalgo et al., 2017]] ).

Changes in mean precipitation rates are less consistent and long-term trends are generally weak. Different databases show significant differences depending mainly on the type and resolution of data ( [[#Centella-Artola--2020|Centella-Artola et al., 2020]] ). Small positive trends were observed in the total annual precipitation ( [[#Stephenson--2014|Stephenson et al., 2014]] ). In SCA and CAR, trends in annual precipitation are generally non-significant, with the exception of small significant positive trends for sub-regions or limited periods ( [[#Planos%20Gutiérrez--2012|Planos Gutiérrez et al., 2012]] ; [[#Hidalgo--2017|Hidalgo et al., 2017]] ), and the 1970–1999 trends in precipitation in SCA are generally non-significant (J.M. [[#Jones--2016|Jones et al., 2016]] ; [[#Hidalgo--2017|Hidalgo et al., 2017]] ). Positive trends in the duration of the MSD have been found in this region over the past four decades ( ''low confidence'' ) ( [[#Anderson--2019|Anderson et al., 2019]] ). For CAR see also [[#Atlas.10|Atlas.10]] Small Islands.

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==== Atlas.7.1.3 Assessment of Model Performance ====

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The ability of climate models to simulate the climate in this region has improved in many key aspects ( [[#Karmalkar--2013|Karmalkar et al., 2013]] ; [[#Fuentes-Franco--2014|Fuentes-Franco et al., 2014]] , [[#Fuentes-Franco--2015|Fuentes-Franco et al., 2015]] , [[#Fuentes-Franco--2017|Fuentes-Franco et al., 2017]] ; [[#Vichot-Llano--2014|Vichot-Llano et al., 2014]] ; [[#Vichot-Llano--2017|Vichot-Llano and Martínez-Castro, 2017]] ; [[#Martínez-Castro--2018|Martínez-Castro et al., 2018]] ). Particularly relevant for this region are increased model resolution and a better representation of the land surface processes ( ''high confidence'' ) ''.''

Regional climate models (RCMs) forced with reanalyses and atmosphere-only global climate models provide simulations with a reasonably good performance over the core North American Monsoon region, mostly in NCA ( ''high confidence'' ) ( [[#Bukovsky--2013|Bukovsky et al., 2013]] ; [[#Cerezo-Mota--2016|Cerezo-Mota et al., 2016]] ). RCMs also reproduce the seasonal spatial patterns of temperature and the bimodal rainfall characteristics of the NCA, SCA and CAR ( ''high confidence'' ) ( [[#Karmalkar--2013|Karmalkar et al., 2013]] ; [[#Centella-Artola--2015|Centella-Artola et al., 2015]] ; [[#Martínez-Castro--2018|Martínez-Castro et al., 2018]] ; [[#Cavazos--2020|Cavazos et al., 2020]] ; [[#Vichot-Llano--2021b|Vichot-Llano et al., 2021b]] ), though in some sub-regions specific models overestimate and shift the month of the maxima. RCM simulations in the region do not necessarily improve with the size of the domain, as important features of the regional circulation and key rainfall climate features, such as the CLLJ and MSD, are well represented for a variety of domains of different sizes ( ''high confidence'' ) ( [[#Centella-Artola--2015|Centella-Artola et al., 2015]] ; [[#Martínez-Castro--2018|Martínez-Castro et al., 2018]] ; [[#Cabos--2019|Cabos et al., 2019]] ; [[#Cavazos--2020|Cavazos et al., 2020]] ; [[#Vichot-Llano--2021b|Vichot-Llano et al., 2021b]] ).

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==== Atlas.7.1.4 Assessment and Synthesis of Projections ====

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Figure Atlas.22 and the Interactive Atlas synthesize regional mean changes in annual mean surface air temperature and precipitation for the Central American reference regions for CMIP6, CMIP5 and CORDEX for different warming levels and time periods. At the 1.5°C GWL, it is ''very likely'' that average annual temperature in Central America over land surpasses 1.3°C (CAR), 1.7°C (NCA) and 1.6°C (SCA). For the 3°C GWL, the corresponding projected ensemble mean regional warming values are 2.7°C (CAR), 3.5°C (NCA) and 3.1°C (SCA). CAR average annual warming is below the level of global warming, while the two continental reference regions are close to the global warming level with CMIP6 and CMIP5 showing very consistent results (Figure Atlas.22). However, when focusing on time slices instead of warming levels, the CMIP6 projections show systematically higher median values than CMIP5. CORDEX results are also consistent with the previous findings, though the subset of driving models spans a smaller range of uncertainty, particularly over CAR. Results have also been reported for this region based on CMIP5, CMIP6 and downscaled simulations over the CORDEX CAM domain or similar smaller domains ( [[#Taylor--2013b|Taylor et al., 2013b]] ; [[#Nakaegawa--2014|Nakaegawa et al., 2014]] ; [[#Imbach--2018|Imbach et al., 2018]] ; [[#Vichot-Llano--2019|Vichot-Llano et al., 2019]] ; [[#Almazroui--2021|Almazroui et al., 2021]] ). Statistical downscaling methods have been also applied to CMIP5 projections to obtain bias-adjusted regional projections ( [[#Colorado-Ruiz--2018|Colorado-Ruiz et al., 2018]] ; [[#Taylor--2018|Taylor et al., 2018]] ; [[#Vichot-Llano--2019|Vichot-Llano et al., 2019]] ).

Global and regional models consistently project warming in the whole region for the end of the century, under RCP4.5 and RCP8.5 for CMIP5 projections with greater warming for continental compared to insular territories, ''likely'' reaching values between 2°C and 4°C ( ''high confidence'' ) ( [[#Campbell--2011|Campbell et al., 2011]] ; [[#Karmalkar--2011|Karmalkar et al., 2011]] ; [[#Cavazos--2012|Cavazos and Arriaga-Ramírez, 2012]] ; [[#Cantet--2014|Cantet et al., 2014]] ; [[#Chou--2014|Chou et al., 2014]] ; [[#Coppola--2014|Coppola et al., 2014]] ; [[#Hidalgo--2017|Hidalgo et al., 2017]] ; [[#Colorado-Ruiz--2018|Colorado-Ruiz et al., 2018]] ; [[#Imbach--2018|Imbach et al., 2018]] ). The greatest warming of 5.8°C for the end of the century was projected for northern Mexico under RCP8.5 ( [[#Colorado-Ruiz--2018|Colorado-Ruiz et al., 2018]] ), using an ensemble of CMIP5 GCMs (Interactive Atlas).

Regarding precipitation, it is ''likely'' that the annual average precipitation changes for the 1.5°C GWL will be in the ranges of –11 to 0% in CAR, from –12 to 0% in SCA, and from –10 to +3% in NCA (Interactive Atlas). For the 3°C GWL, the corresponding annual average precipitation changes will be from –17 to –2% in CAR, from –16 to +2% in NCA, and from –23 to 0% in SCA. A clear drying tendency is observed for the 3°C GWL relative to the 1.5°C GWL. [[#Maloney--2014|Maloney et al. (2014)]] examined 21st-century climate projections of North American climate in CMIP5 models under RCP8.5, including Central America and the Caribbean. Summer drying was projected in CAR and SCA for most of the models, with good agreement. The strongest drying is projected to occur during July and August which are the months when the MSD occurs in many sub-regions (Figure Atlas.22 and the Interactive Atlas). Intensification of the MSD in SCA was also projected by using the Rossby Centre Regional Climate Model (RCA4; [[#Corrales-Suastegui--2020|Corrales-Suastegui et al., 2020]] ), but with a future decrease in area and frequency (Cross-Chapter Box [[#Atlas.2|Atlas.2]] ). They also found a projected intensification of CLLJ and drying for the future time slice of 2071–2095, relative to their baseline of 1981–2005. Decreased precipitation was also projected for SCA ( [[#Imbach--2018|Imbach et al., 2018]] ) with the 8-km resolution Eta RCM during the rainy season, including an intensification of the MSD, although no significant change was projected for the CLLJ.

[[#Colorado-Ruiz--2018|Colorado-Ruiz et al. (2018)]] assessed an ensemble of 14 GCMs from CMIP5 for a 1971–2000 baseline period, projecting precipitation decreases of between 5% and 10% by the end of the century for the RCP4.5 and RCP8.5 scenarios respectively. The greatest decrease in precipitation is projected during summer reaching 13%, especially in southern Mexico, Central America and the Caribbean. Dynamically downscaled simulations ( [[#Bukovsky--2015|Bukovsky et al., 2015]] ) also projected a decrease of precipitation for the middle of the century (2041–2069) relative to 1971–1999 for the north of Mexico, though despite good agreement amongst the models, these results must be considered of ''low confidence'' , because of their poor simulation of important monsoon physical processes. [[#Vichot-Llano--2021a|Vichot-Llano et al. (2021a)]] used a multi-parameter ensemble of RegCM4, driven by the CMIP5 global model HagGEM2-ES projections to conclude that, relative to the 1975–2004 baseline, in the near (2020–2049) and more prominently in the far (2070–2099) future, drier conditions will prevail at over the eastern Caribbean. The projected future warming trend was statistically significant at the 95% confidence level over CAR and SCA. [[#Almazroui--2021|Almazroui et al. (2021)]] used an ensemble of 31 CMIP6 models to estimate climate change signals of temperature and precipitation in six reference regions in North and Central America and the Caribbean, finding a decrease in precipitation (10–30%) over Central America and the Caribbean under three scenarios with regional and seasonal variations.

There is ''high agreement'' and ''high confidence'' in the projected decrease of precipitation by the end of the century for most of the region, particularly for annual and summer precipitation, but there is ''low confidence'' on the magnitude of this decrease which varies between 5% and 50% for different projections and different sub-regions (see extended information in the Interactive Atlas).

The status of climateextreme trends and projections for the region has been assessed in [[IPCC:Wg1:Chapter:Chapter-11|Chapter 11]] and the main findings are synthesized here. There is ''high confidence'' in the projections of significant heatwave events at the end of the century in SCA ( [[#Angeles-Malaspina--2018|Angeles-Malaspina et al., 2018]] ) and an increase in warm days and warm nights over this region and CAR (Stennett- [[#Brown--2017|Brown et al., 2017]] ). For CAR islands, using dynamically downscaled CMIP3 models, [[#Karmalkar--2013|Karmalkar et al. (2013)]] projected an increase in drought severity at the end of the century, mainly due to a precipitation decrease during the early wet season. In SCA, projections suggest an increase in the MSD ( [[#Imbach--2018|Imbach et al., 2018]] ) and an increase in consecutive dry days ( [[#Chou--2014|Chou et al., 2014]] ), consistent with the projections of Stennett- [[#Brown--2017|Brown et al. (2017)]] .

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==== Atlas.7.1.5 Summary ====

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Significant warming trends between 0.2°C and 0.3°C per decade have been observed in the three reference regions of Central America in the last 30 years, with the largest increases in the North American Monsoon region ( ''high confidence'' ) ''.'' Changes in mean precipitation rates are less consistent and long-term trends are generally weak. Small positive trends were observed in the total annual precipitation in part of the region.

Warming in the continental part of the region is projected to increase in the range of the mean global values for GWL of 1.5°C and 3°C, but in the Caribbean regional warming will be lower. Precipitation is projected to decrease with increasing GWLs, especially for CAR and SCA.

Projected change in mean annual precipitation shows a large spatial variability across Central America and the Caribbean. Under moderate future emissions overall negative but non-significant precipitation trends are projected for the 21st century ( ''low confidence'' ). Under higher-emissions scenarios and at higher GWLs, average precipitation is ''likely'' to decrease in most of the region, particularly in the north-western and central Caribbean and part of continental Central America, especially in SCA.

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