{"id":467057,"date":"2026-08-30T05:11:46","date_gmt":"2026-08-30T12:11:46","guid":{"rendered":"https:\/\/climatescience.press\/?p=467057"},"modified":"2026-08-30T05:11:48","modified_gmt":"2026-08-30T12:11:48","slug":"ancient-tropical-forests-reveal-ice-age-earth-was-5-4c-colder","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=467057","title":{"rendered":"Ancient Tropical Forests Reveal Ice Age Earth Was 5.4\u00b0C Colder"},"content":{"rendered":"\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"723\" height=\"485\" data-attachment-id=\"467058\" data-permalink=\"https:\/\/climatescience.press\/?attachment_id=467058\" data-orig-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?fit=1168%2C784&amp;ssl=1\" data-orig-size=\"1168,784\" data-comments-opened=\"1\" 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data-image-title=\"0 Ancient Tropical Forests Reveal Ice Age Earth Was 5.4\u00b0C Colder\" data-image-description=\"\" data-image-caption=\"&lt;p&gt;Signature: 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&lt;\/p&gt;\n\" data-large-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?fit=723%2C485&amp;ssl=1\" src=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?resize=723%2C485&#038;ssl=1\" alt=\"\" class=\"wp-image-467058\" srcset=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?resize=1024%2C687&amp;ssl=1 1024w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?resize=300%2C201&amp;ssl=1 300w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?resize=768%2C516&amp;ssl=1 768w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?resize=640%2C430&amp;ssl=1 640w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?w=1168&amp;ssl=1 1168w\" sizes=\"auto, (max-width: 723px) 100vw, 723px\" \/><figcaption class=\"wp-element-caption\">AI generated by Grok<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A recent 2026 study in Geophysical Research Letters (Hou et al.) estimates that global mean surface temperature during the Last Glacial Maximum (LGM, ~20,000- 21,000 years ago) was about 5.4\u00b0C colder than today, based on tropical land cooling constraints combined with climate model relationships.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Researchers compiled a multiproxy dataset of 61 tropical\/subtropical (low- to mid-latitude) land temperature records from pollen assemblages, noble gases in ancient groundwater, glacial evidence (e.g., equilibrium line altitudes), and other proxies. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">They estimated tropical land cooling of roughly 4.2\u00b0C relative to the present. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Using emergent relationships from 13 state-of-the-art LGM climate model simulations (linking tropical land temperatures, tropical sea-surface temperatures, and global mean temperature), they inferred <strong>tropical ocean cooling of about 2.6\u00b0C <\/strong>and the <strong>global figure of ~5.4\u00b0C.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A closely related preprint by the same group reported somewhat <strong>stronger cooling<\/strong> (tropical land \u22124.8\u00b0C with 95% CI \u22125.6 to \u22124.0\u00b0C; tropical SST \u22122.9\u00b0C; global mean \u22125.9\u00b0C with 95% CI \u22127.3 to \u22124.7\u00b0C), suggesting the published numbers reflect refinements.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Many earlier reconstructions (including those relying heavily on the <strong>MARGO<\/strong> <strong>sea-surface temperature<\/strong> compilation) suggested <strong>milder global cooling<\/strong>, often in the ~4- 5\u00b0C range or less for the tropics.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Stronger cooling estimates exist:<\/strong> Wikipedia notes ~6\u00b0C global average; a 2020 data-assimilation study (Tierney et al.) found \u22126.1\u00b0C (95% CI \u22126.5 to \u22125.7\u00b0C); noble-gas groundwater studies indicate low-to-mid-latitude land cooling of ~5.8\u00b0C (\u00b10.6\u00b0C).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Tropical cooling has long been debated. <strong>Older CLIMAP reconstructions <\/strong>suggested limited tropical ocean cooling, but land proxies (pollen shifts, snowlines, noble gases from sites like Brazil) and some ocean proxies have repeatedly indicated larger changes (~5\u00b0C or more on tropical land in places).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The new work places the LGM toward the colder end of published ranges.<\/strong> <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Because LGM CO\u2082 was much lower (~180- 200 ppm vs. pre-industrial ~280 ppm), a larger temperature drop implies higher equilibrium climate sensitivity (warming per CO\u2082 doubling).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The results make very low sensitivity (ECS \u2272 ~3\u00b0C) less likely and help constrain models that underproduce glacial cooling.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Uncertainties remain:<\/strong> proxy scatter, dating precision, local effects, and the fact that the global number is inferred via model relationships rather than directly observed everywhere.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The approach is presented as adaptable to other periods or variables. Overall, it reinforces that the tropics experienced substantial cooling during the LGM peak and that the global climate system responded strongly to the lower greenhouse- gas levels and expanded ice sheets of that time.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">_____________________________________________________________________________________<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Tropical land temperature proxies, essentially an \u201cancient jungle thermometer\u201d, can be used to constrain global cooling during the Last Glacial Maximum (LGM, ~20,000\u201321,000 years ago), as shown in the 2026 study by Hou et al. published in Geophysical Research Letters.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Tropical regions (roughly 30\u00b0S\u201330\u00b0N) preserve a variety of climate proxies that record past land temperatures:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Pollen and vegetation assemblages (shifts in plant communities that track temperature and moisture).<\/li>\n\n\n\n<li>Noble gases dissolved in ancient groundwater.<\/li>\n\n\n\n<li>Glacial evidence such as equilibrium-line altitudes of tropical mountain glaciers.<\/li>\n\n\n\n<li>Other indicators (e.g., certain geochemical or fossil records).<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">These provide relatively direct estimates of how much cooler tropical land surfaces were during the LGM compared with today. Because the tropics cover a large fraction of Earth\u2019s surface and respond more uniformly than high-latitude regions dominated by ice sheets, they offer a useful anchor for global temperature reconstructions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The researchers compiled a multiproxy dataset of tropical land temperature reconstructions and combined it with an ensemble of climate model simulations of the LGM. Within those models they identified stable statistical (\u201cemergent\u201d) relationships connecting:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Tropical land temperature change,<\/li>\n\n\n\n<li>Tropical sea-surface temperature change, and<\/li>\n\n\n\n<li>Global mean surface temperature change.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">They then applied the observed tropical land cooling to these relationships. Results from the study (and its preprint) indicate:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Tropical land cooled by roughly 4.2\u20134.8 \u00b0C,<\/li>\n\n\n\n<li>Tropical oceans cooled by about 2.6\u20132.9 \u00b0C,<\/li>\n\n\n\n<li>Global mean surface temperature was approximately<strong> 5.4\u20135.9 \u00b0C <\/strong>colder than today.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">These figures place the LGM toward the colder end of recent estimates and are colder than many reconstructions that relied heavily on earlier sea-surface temperature compilations such as MARGO.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A larger LGM temperature drop under substantially lower atmospheric CO\u2082 implies a more sensitive climate system (higher equilibrium climate sensitivity).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>tropical \u201cthermometer\u201d<\/strong> therefore helps tighten constraints on how strongly Earth\u2019s climate responds to greenhouse-gas changes, while also offering a transferable method that can be applied to other time periods once sufficient proxy data exist.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">An ancient tropical land- temperature record can serve as a practical thermometer that, when combined with model relationships, reveals the scale of the global chill during the peak of the last Ice Age.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">_____________________________________________________________________________________<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>MARGO<\/strong> stands for <strong>Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface.<\/strong> It is a major international collaborative project (supported by IMAGES and PAGES) that produced one of the most influential reconstructions of <strong>sea- surface temperatures (SSTs)<\/strong> during the <strong>Last Glacial Maximum (LGM).<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The primary synthesis was published in 2009 by the MARGO Project Members (led by C. Waelbroeck and colleagues) in Nature Geoscience:<br><strong>\u201cConstraints on the magnitude and patterns of ocean cooling at the Last Glacial Maximum\u201d <\/strong>(doi:10.1038\/ngeo411).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Time interval:<\/strong> Strictly defined as 23\u201319 thousand years before present (following the EPILOG definition), narrower and more rigorous than the broader window used by the earlier CLIMAP project.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Proxies used (multiproxy philosophy):<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Microfossil assemblage transfer functions (planktonic foraminifera, diatoms, dinoflagellate cysts, radiolarians).<\/li>\n\n\n\n<li>Geochemical proxies (alkenone unsaturation index <math xmlns=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><semantics style=\"color: black; background-color: transparent; font-family: sans-serif;\"><mrow style=\"color: black; background-color: transparent; font-family: sans-serif;\"><msubsup style=\"color: black; background-color: transparent; font-family: sans-serif;\"><mi style=\"color: black; background-color: transparent; font-family: sans-serif;\">U<\/mi><mn style=\"color: black; background-color: transparent; font-family: sans-serif;\">37<\/mn><mi style=\"color: black; background-color: transparent; font-family: sans-serif;\">k<\/mi><\/msubsup><\/mrow><annotation encoding=\"application\/x-tex\" style=\"color: black; background-color: transparent; font-family: sans-serif;\">U^k_{37}<\/annotation><\/semantics><\/math><code>U^k_{37}<\/code> and Mg\/Ca ratios in planktonic foraminifera).<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Data volume:<\/strong> Approximately 696 individual SST reconstructions from sediment cores worldwide.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Proxies used (multiproxy philosophy):\n<ul class=\"wp-block-list\">\n<li>Microfossil assemblage transfer functions (planktonic foraminifera, diatoms, dinoflagellate cysts, radiolarians).<\/li>\n\n\n\n<li>Geochemical proxies (alkenone unsaturation index <math xmlns=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><semantics style=\"color: black; background-color: transparent; font-family: sans-serif;\"><mrow style=\"color: black; background-color: transparent; font-family: sans-serif;\"><msubsup style=\"color: black; background-color: transparent; font-family: sans-serif;\"><mi style=\"color: black; background-color: transparent; font-family: sans-serif;\">U<\/mi><mn style=\"color: black; background-color: transparent; font-family: sans-serif;\">37<\/mn><mi style=\"color: black; background-color: transparent; font-family: sans-serif;\">k<\/mi><\/msubsup><\/mrow><annotation encoding=\"application\/x-tex\" style=\"color: black; background-color: transparent; font-family: sans-serif;\">U^k_{37}<\/annotation><\/semantics><\/math><code>U^k_{37}<\/code> and Mg\/Ca ratios in planktonic foraminifera).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The project emphasized that no single proxy is superior; combining them with quality assessments produces a more robust picture. Data were calibrated against a common modern temperature dataset and quality- controlled, with reliability flags assigned to individual records.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>MARGO revealed stronger and more structured cooling than many earlier views:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Strongest annual-mean cooling (up to \u221210\u00b0C) occurred in the mid-latitude North Atlantic, with a steep temperature gradient between ~45\u00b0N and 60\u00b0N.<\/li>\n\n\n\n<li>Cooling was more pronounced in the eastern than the western North Atlantic (contrasting with some CLIMAP patterns).<\/li>\n\n\n\n<li>Tropical oceans (30\u00b0S\u201330\u00b0N) showed heterogeneous cooling, generally larger and more extensive than in CLIMAP, with greater cooling in the tropical Atlantic than in the Indian or Pacific. Western Pacific Warm Pool cooling was modest (roughly 1\u20133\u00b0C).<\/li>\n\n\n\n<li>Large longitudinal (east\u2013west) SST gradients existed in all major ocean basins\u2014features not well captured by the climate models available at the time.<\/li>\n\n\n\n<li>Some limited regions showed relative warmth or minimal cooling (e.g., parts of the northwest Australian margin), attributed to changes in ocean circulation.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Basin- averaged annual-mean cooling estimates (from the multiproxy dataset) were on the order of roughly \u22121.5 to \u22122.5\u00b0C depending on the ocean, with substantial spatial variability and uncertainty. Global tropical cooling was relatively modest compared with some later land-based or data- assimilation reconstructions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Comparison with CLIMAP and Later Work<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>vs. CLIMAP (1970s\u20131980s):<\/strong> MARGO improved temporal definition, data density (especially in the North Atlantic and tropics), multiproxy integration, and quality control. It showed more heterogeneous tropical cooling and different longitudinal patterns.<\/li>\n\n\n\n<li><strong>Influence and limitations:<\/strong> MARGO became a standard benchmark for evaluating paleoclimate models (e.g., PMIP) and for estimating climate sensitivity. However, its relatively modest tropical and global-mean cooling has been criticized or revised by later work. Some studies argue it underestimates cooling in certain regions due to proxy limitations, calibration issues, or sparse coverage (especially in the Pacific and Southern Ocean). Newer compilations (e.g., TEA20) and data-assimilation products that blend proxies with models often indicate stronger overall LGM cooling (global SST anomalies closer to \u22123\u00b0C or more in some reconstructions).<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The MARGO dataset (including gridded products on a 5\u00b0 \u00d7 5\u00b0 grid, individual site data, and reliability assessments) is publicly archived at:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NOAA\/NCEI World Data Service for Paleoclimatology.<\/li>\n\n\n\n<li>PANGAEA.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">It remains widely used as a foundational reference, even as researchers develop updated multiproxy compilations and model- data fusion approaches that incorporate additional proxies and address spatial gaps.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In the broader context of LGM climate research and equilibrium climate sensitivity debates, MARGO\u2019s relatively mild tropical cooling has historically supported lower- to- moderate sensitivity estimates.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">More recent reconstructions that find stronger tropical and global cooling (including some land- proxy and emergent- constraint studies) tend to favor higher sensitivity values once pattern effects and other forcings are accounted for.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">_____________________________________________________________________________________<\/p>\n\n\n\n<p class=\"has-large-font-size wp-block-paragraph\"><strong>\u201cReassessing Last Glacial Maximum Cooling With Proxy-Constrained Emergent Relationships\u201d<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The study addresses the challenge of reconstructing global temperatures from sparse, unevenly distributed paleoclimate proxy data. It applies an <strong>emergent constraint framework:<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Researchers assembled a new multiproxy dataset of tropical land temperature reconstructions for the Last Glacial Maximum (LGM, roughly 20-21 ka).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">They identified robust statistical (\u201cemergent\u201d) relationships in an ensemble of paleoclimate model simulations linking tropical land temperature change, tropical sea- surface temperature (SST) change, and global mean surface temperature change.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Proxy- based tropical land cooling was then used to constrain the harder- to-observe tropical SST and global mean values.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">From the preprint abstract:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Tropical terrestrial (land) temperature change:<strong> \u22124.8\u00b0C<\/strong> (95% CI: \u22125.6 to \u22124.0\u00b0C).<\/li>\n\n\n\n<li>Constrained tropical SST change: <strong>\u22122.9\u00b0C<\/strong> (95% CI: \u22123.6 to \u22122.3\u00b0C).<\/li>\n\n\n\n<li>Constrained global mean surface temperature change: <strong>\u22125.9\u00b0C<\/strong> (95% CI: \u22127.3 to \u22124.7\u00b0C).<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">A contemporaneous news summary of the published paper reported slightly milder central values (tropical land \u2248 \u22124.2\u00b0C, tropical oceans \u2248 \u22122.6\u00b0C, global \u2248 \u22125.4\u00b0C), still pointing to relatively strong LGM cooling.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">These estimates indicate a colder LGM climate than reconstructions that rely heavily on the MARGO SST compilation (which generally suggested milder tropical ocean cooling).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Broader Implications<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The results support stronger glacial cooling, consistent with some independent lines of evidence (e.g., noble- gas groundwater studies showing substantial low-latitude land cooling).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Stronger LGM cooling (under substantially lower CO\u2082 concentrations) tends to favor higher equilibrium climate sensitivity (ECS) and makes very low ECS values less plausible.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The authors emphasize that the emergent- constraint approach is flexible and can be adapted to other time periods or climate variables once sufficient proxy data and model ensembles are available.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The paper uses tropical land proxies plus model- derived relationships to argue for relatively large LGM cooling (centered around 5.4- 5.9\u00b0C globally), placing the LGM toward the colder end of recent estimates and providing a transferable methodological framework for paleoclimate reconstruction.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Published:<\/strong> Geophysical Research Letters<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>DOI:<\/strong> <a href=\"https:\/\/dx.doi.org\/10.1029\/2026gl123083\" target=\"_blank\" rel=\"noopener\">10.1029\/2026gl123083<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Authors:<\/strong> Alicia Hou and colleagues (Thibaut Caley, Thomas Extier, Manuel Chevalier, Mathilde Brug\u00e8re, Didier Swingedouw, Masa Kageyama, and Pascale Braconnot)<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Abstract<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Reconstructing global temperatures from sparse proxy data remains a key uncertainty in paleoclimate science. Here, we apply an emergent constraint framework that combines statistical relationships from paleoclimate model simulations with proxy-based estimates to infer unknown climate variables. We compiled a new multiproxy data set of tropical land temperature reconstructions for the Last Glacial Maximum (LGM), which implies tropical terrestrial cooling of \u22124.2\u00b0C (\u22125.0 to \u22123.5\u00b0C, 95% Confidence Interval, CI). Applying our emergent constraint framework to this terrestrial temperature reconstruction, we derived updated estimates of tropical sea surface temperature (\u22122.6\u00b0C; \u22123.3 to \u22122.0\u00b0C, 95% CI) and global mean surface temperature (\u22125.4\u00b0C; \u22126.5 to \u22124.4\u00b0C, 95% CI). These observation-based estimates support LGM cooling toward the colder end of published ranges, implying that very low equilibrium climate sensitivity (ECS &lt; \u223c3\u00b0C) is unlikely. Our method is adaptable for different time periods and climate variables, providing a flexible framework for integrating proxy and model information.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>ropical land temperature proxies, essentially an \u201cancient jungle thermometer\u201d, can be used to constrain global cooling during the Last Glacial Maximum (LGM, ~20,000\u201321,000 years ago), as shown in the 2026 study by Hou et al. published in Geophysical Research Letters.<\/p>\n","protected":false},"author":121246920,"featured_media":467058,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"jetpack_seo_schema_type":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_wpcom_ai_launchpad_first_post":false,"_jetpack_hide_featured_image":false,"_jetpack_featured_image_duplicate_dismissed":0,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"Tropical land temperature proxies, essentially an \"ancient jungle thermometer\", can be used to constrain global cooling during the Last Glacial Maximum (LGM, ~20,000\u201321,000 years ago), as shown in the 2026 study by Hou et al. published in Geophysical Research Letters.","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1],"tags":[691845046,691836612,691845044,691828456,691839752],"class_list":["post-467057","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-land-temperature-records","tag-last-glacial-maximum-lgm","tag-margo","tag-ocean-cooling","tag-sea-surface-temperature-sst-2","fallback-thumbnail"],"jetpack_publicize_connections":[],"jetpack_likes_enabled":true,"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/paxLW1-1Xvb","jetpack-related-posts":[{"id":462891,"url":"https:\/\/climatescience.press\/?p=462891","url_meta":{"origin":467057,"position":0},"title":"Tropical Cooling Reveals Last Ice Age Was 5.4\u00b0C Colder Than Today","author":"uwe.roland.gross","date":"08\/14\/2026","format":false,"excerpt":"The Last Glacial Maximum was the peak of the most recent glacial period (Late Pleistocene), when continental ice sheets reached their greatest volume and extent. It is one of the best-studied past climate states and a critical benchmark for understanding climate sensitivity, ice-sheet dynamics, and global climate feedbacks.","rel":"","context":"In \"global mean surface temperature (GMST)\"","block_context":{"text":"global mean surface temperature (GMST)","link":"https:\/\/climatescience.press\/?tag=global-mean-surface-temperature-gmst"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Tropical-Cooling-Reveals-Last-Ice-Age-Was-5.4%C2%B0C-Colder-Than-Today.jpg?fit=1168%2C784&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Tropical-Cooling-Reveals-Last-Ice-Age-Was-5.4%C2%B0C-Colder-Than-Today.jpg?fit=1168%2C784&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Tropical-Cooling-Reveals-Last-Ice-Age-Was-5.4%C2%B0C-Colder-Than-Today.jpg?fit=1168%2C784&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Tropical-Cooling-Reveals-Last-Ice-Age-Was-5.4%C2%B0C-Colder-Than-Today.jpg?fit=1168%2C784&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Tropical-Cooling-Reveals-Last-Ice-Age-Was-5.4%C2%B0C-Colder-Than-Today.jpg?fit=1168%2C784&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":480331,"url":"https:\/\/climatescience.press\/?p=480331","url_meta":{"origin":467057,"position":1},"title":"Ice Age Humans in New Mexico Endured Sudden Climate Chaos 23,000 Years Ago","author":"uwe.roland.gross","date":"10\/19\/2026","format":false,"excerpt":"New research from White Sands National Park in New Mexico shows that early humans were present during the Last Glacial Maximum (roughly 23,500- 21,700 years ago) and lived through repeated, rapid climate shifts, including drought and major landscape changes. Dansgaard- Oeschger (D-O) events are abrupt, large- scale climate oscillations that\u2026","rel":"","context":"In \"ancient Lake Otero\"","block_context":{"text":"ancient Lake Otero","link":"https:\/\/climatescience.press\/?tag=ancient-lake-otero"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/10\/0-Ice-Age-Humans-in-New-Mexico-Endured-Sudden-Climate-Chaos-23000-Years-Ago.jpg?fit=1168%2C784&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/10\/0-Ice-Age-Humans-in-New-Mexico-Endured-Sudden-Climate-Chaos-23000-Years-Ago.jpg?fit=1168%2C784&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/10\/0-Ice-Age-Humans-in-New-Mexico-Endured-Sudden-Climate-Chaos-23000-Years-Ago.jpg?fit=1168%2C784&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/10\/0-Ice-Age-Humans-in-New-Mexico-Endured-Sudden-Climate-Chaos-23000-Years-Ago.jpg?fit=1168%2C784&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/10\/0-Ice-Age-Humans-in-New-Mexico-Endured-Sudden-Climate-Chaos-23000-Years-Ago.jpg?fit=1168%2C784&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":463941,"url":"https:\/\/climatescience.press\/?p=463941","url_meta":{"origin":467057,"position":2},"title":"Milankovitch Cycles, the Last Glacial Period, and Why Earth Is Still in an Ice Age","author":"uwe.roland.gross","date":"08\/19\/2026","format":false,"excerpt":"The Holocene has been relatively stable and warm by glacial-cycle standards, which is one reason human civilization developed during it. Orbital (Milankovitch) forcing would eventually lead toward the next glacial period over tens of thousands of years in the absence of other influences, but elevated greenhouse-gas levels are expected to\u2026","rel":"","context":"In \"Holocene interglacial\"","block_context":{"text":"Holocene interglacial","link":"https:\/\/climatescience.press\/?tag=holocene-interglacial"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Milankovitch-Cycles-the-Last-Glacial-Period-and-Why-Earth-Is-Still-in-an-Ice-Age.jpg?fit=1168%2C784&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Milankovitch-Cycles-the-Last-Glacial-Period-and-Why-Earth-Is-Still-in-an-Ice-Age.jpg?fit=1168%2C784&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Milankovitch-Cycles-the-Last-Glacial-Period-and-Why-Earth-Is-Still-in-an-Ice-Age.jpg?fit=1168%2C784&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Milankovitch-Cycles-the-Last-Glacial-Period-and-Why-Earth-Is-Still-in-an-Ice-Age.jpg?fit=1168%2C784&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Milankovitch-Cycles-the-Last-Glacial-Period-and-Why-Earth-Is-Still-in-an-Ice-Age.jpg?fit=1168%2C784&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":367383,"url":"https:\/\/climatescience.press\/?p=367383","url_meta":{"origin":467057,"position":3},"title":"What Really Sets the Global Climate State?","author":"uwe.roland.gross","date":"02\/24\/2025","format":false,"excerpt":"What really does set the global climate state? The Million Year Ice Core Project (MYIC) (Follow on BlueSky), has been underway for several years, preparing to drill the oldest continuous ice core record from Antarctica. The project is a major element in the Australian Antarctic Program, led by the Australian\u2026","rel":"","context":"In \"Antarctica\"","block_context":{"text":"Antarctica","link":"https:\/\/climatescience.press\/?tag=antarctica"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/02\/0ice-core-scientist-in-the-field.1600x0.jpg?fit=1200%2C800&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/02\/0ice-core-scientist-in-the-field.1600x0.jpg?fit=1200%2C800&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/02\/0ice-core-scientist-in-the-field.1600x0.jpg?fit=1200%2C800&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/02\/0ice-core-scientist-in-the-field.1600x0.jpg?fit=1200%2C800&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/02\/0ice-core-scientist-in-the-field.1600x0.jpg?fit=1200%2C800&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":426251,"url":"https:\/\/climatescience.press\/?p=426251","url_meta":{"origin":467057,"position":4},"title":"Holocene Glacier Records","author":"uwe.roland.gross","date":"02\/14\/2026","format":false,"excerpt":"Glacier length changes through time, they advance when the local climate around them is colder and retreat when it is warmer (Bray, 1968). Over century and greater time scales glacier length is considered a highly reliable indicator of both regional and worldwide warming trends according to Olga Solomina, Johannes Oerlemans,\u2026","rel":"","context":"In \"Atlantic Multidecadal Oscillation (AMO)\"","block_context":{"text":"Atlantic Multidecadal Oscillation (AMO)","link":"https:\/\/climatescience.press\/?tag=atlantic-multidecadal-oscillation-amo"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/02\/00Screenshot-2026-02-14-220345.png?fit=1200%2C606&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/02\/00Screenshot-2026-02-14-220345.png?fit=1200%2C606&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/02\/00Screenshot-2026-02-14-220345.png?fit=1200%2C606&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/02\/00Screenshot-2026-02-14-220345.png?fit=1200%2C606&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/02\/00Screenshot-2026-02-14-220345.png?fit=1200%2C606&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":287036,"url":"https:\/\/climatescience.press\/?p=287036","url_meta":{"origin":467057,"position":5},"title":"Hansen\u2019s latest overheated global warming claims are based on poor science","author":"uwe.roland.gross","date":"11\/07\/2023","format":false,"excerpt":"James Hansen is warning that the world isn\u2019t just steadily warming but is dangerously accelerating, according to a study that some other scientists call overheated. From Climate Etc. By\u00a0niclewis\u00a0 James Hansen\u2019s latest\u00a0paper\u00a0\u201cGlobal warming in the pipeline\u201d (Hansen et al. (2023)) has already been heavily criticized in a lengthy\u00a0comment\u00a0by Michael Mann,\u2026","rel":"","context":"In \"CO2\"","block_context":{"text":"CO2","link":"https:\/\/climatescience.press\/?tag=co2"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/OIG-2023-08-04T125905.505.jpeg?fit=1024%2C1024&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/OIG-2023-08-04T125905.505.jpeg?fit=1024%2C1024&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/OIG-2023-08-04T125905.505.jpeg?fit=1024%2C1024&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/OIG-2023-08-04T125905.505.jpeg?fit=1024%2C1024&ssl=1&resize=700%2C400 2x"},"classes":[]}],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/08\/0-Ancient-Tropical-Forests-Reveal-Ice-Age-Earth-Was-5.4%C2%B0C-Colder.jpg?fit=1168%2C784&ssl=1","_links":{"self":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts\/467057","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/users\/121246920"}],"replies":[{"embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=467057"}],"version-history":[{"count":35,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts\/467057\/revisions"}],"predecessor-version":[{"id":467093,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts\/467057\/revisions\/467093"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/media\/467058"}],"wp:attachment":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=467057"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=467057"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=467057"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}