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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Past records help to predict different effects of future climate change   
   on land and sea    
      
     Date:   
         February 8, 2023   
     Source:   
         Woods Hole Oceanographic Institution   
     Summary:   
         Ongoing climate change driven by greenhouse gas emissions is   
         often discussed in terms of global average warming. For example,   
         the landmark Paris Agreement seeks to limit global warming to 1.5   
         degrees C, relative to pre-industrial levels. However, the extent   
         of future warming will not be the same throughout the planet. One   
         of the clearest regional differences in climate change is the   
         faster warming over land than sea.   
      
         This 'terrestrial amplification' of future warming has real-world   
         implications for understanding and dealing with climate change.   
      
      
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   FULL STORY   
   ==========================================================================   
   Ongoing climate change driven by greenhouse gas emissions is often   
   discussed in terms of global average warming. For example, the landmark   
   Paris Agreement seeks to limit global warming to 1.5 ?C, relative to   
   pre-industrial levels.   
      
   However, the extent of future warming will not be the same throughout   
   the planet. One of the clearest regional differences in climate change is   
   the faster warming over land than sea. This "terrestrial amplification"   
   of future warming has real-world implications for understanding and   
   dealing with climate change   
      
   ==========================================================================   
   A new paper studying terrestrial amplification focuses on how geochemical   
   records of past climate on land and at the sea surface allow scientists   
   to better predict the extent to which land will warm more than oceans   
   -- and will also get drier -- due to current and future greenhouse gas   
   emissions. "The core idea of our study was to look to the past to better   
   predict how future warming will unfold differently over land and sea,"   
   says Alan Seltzer, an assistant scientist in the Marine Chemistry and   
   Geochemistry Department at the Woods Hole Oceanographic Institution   
   (WHOI) and the lead author of the paper.   
      
   "One reason why understanding terrestrial amplification matters is that   
   under future global warming, the magnitude of warming that the planet will   
   experience is not going to be the same everywhere," says Seltzer. "Adding   
   a firm basis to climate model simulations, that is rooted in observations   
   of past climate and basic physics, can tell us about how the regional   
   differences in ongoing and future warming." Seltzer notes that terrestrial   
   amplification (TA) is analogous to "polar amplification," a prediction   
   of climate models that higher latitudes will experience more warming   
   than low latitudes.   
      
   Although modern observational records are noisy due to big year-to-year   
   variations driven by other parts of the climate system, the prediction of   
   greater warming over land surfaces is now apparent in climate data since   
   the 1980s. The drivers of this terrestrial amplification have been linked   
   to changes in moisture over land and sea, through a theory developed   
   by climate scientists over the past decade. This new study, published   
   Wednesday in the journal Science Advances, "uses paleoclimate data for   
   the first time to evaluate the theory for how land and sea surfaces will   
   be impacted by future warming," Seltzer says. "The research gives us more   
   certainty in the way models predict regional changes in future warming."   
   The paper investigates terrestrial amplification during the Last Glacial   
   Maximum (LGM) -- which occurred about 20,000 years ago -- in the low   
   latitudes, which they define as 30?S-30?N. It is in those latitudes, the   
   authors say, where the theoretical basis for TA is most applicable. The   
   authors drew on new compilations of paleoclimate records on land and from   
   the sea surface to estimate the magnitude of TA in the LGM, to compare   
   with climate model simulations and theoretical expectations. Efforts to   
   better understand how cold the continents were in the LGM are an ongoing   
   focus of Seltzer's research at WHOI, and this new paper builds upon a   
   recent study that used insights from dissolved gases trapped in ancient   
   groundwater as a thermometer for the past land surface.   
      
   The authors extended a thermodynamic theory for terrestrial amplification   
   that is based on coupled changes in moist static energy (the potential   
   energy represented by the temperature, moisture content, and elevation of   
   a parcel of air) between land and sea. In the LGM, when sea level was 120   
   meters lower than today due to the growth of large ice sheets on land,   
   the sea surface was slightly warmer and more humid than it would have   
   been without a change in sea level. By taking this effect into account   
   and drawing on paleoclimate records, the authors were able to directly   
   compare past terrestrial amplification to future predictions. The paper   
   notes that while the mechanisms underlying TA are well understood to   
   arise from fundamental thermodynamic differences between humid air   
   over the ocean and drier air over land, a number of factors - - natural   
   variability, observational limitations, thermal lags, and non-CO2 forcings   
   -- have previously precluded a precise estimate of TA from 20th century   
   warming. "Narrowing the range of terrestrial amplification will aid in   
   future predictions of low latitude climate change, with relevance to   
   both heat stress and water availability," the paper states.   
      
   Co-author Pierre-Henri Blard says the paper is a "step forward for   
   climate science," and it will be significant for other scientific fields   
   and the general public. "We show that a simple model, involving humidity   
   and sea level changes, robustly describes the amplification of temperature   
   changes over the continent -- at low to mid-latitudes at any time scale --   
   as being 40% larger than over the ocean. This result is important because,   
   while most paleoclimatic archives are located in the ocean, the present   
   and future of humanity crucially rely on our knowledge of continental   
   climates," says Blard, a Director of Research at the National Center for   
   Scientific Research (CNRS) at the Center for Petrographic and Geochemical   
   Research (CRPG) in Nancy, France.   
      
   The research is important "because it helps us make sense of Earth's past   
   climate record and how to relate it to our models and expectations for   
   the future," co-author Steven Sherwood says. The paper "should clear up   
   any misconceptions that land and ocean warm or cool at the same rate in   
   different climates -- we know otherwise and should use that knowledge. The   
   implications for the future are that Earth's continents will continue to   
   warm faster than the oceans as global warming continues, until hopefully   
   we reach net zero and bring this to a stop," says Sherwood, a professor   
   in the ARC Centre of Excellence for Climate Extremes in the University   
   of New South Wales's Climate Change Research Center, Sydney, Australia.   
      
   Co-author Masa Kageyama says she considers the paper important "because it   
   touches on a feature which is ubiquitous in climate change projections,   
   produced by complex climate models: continents warm more than oceans. In   
   this paper, we analyze this feature for a climate change, from the   
   last glacial maximum to present, the amplitude of which is of the same   
   order of magnitude as the expected warming in the next centuries,"   
   says Kageyama, director of research at CNRS' Climate and Environment   
   Sciences Laboratory (LSCE) at the Pierre Simon Laplace Institute at the   
   University of Paris-Saclay, France.   
      
   "It is remarkable that tropical temperature reconstructions,   
   state-of-the-art climate models, and a simple theory relying on the   
   coupled changes of moisture and heat over continents and oceans all   
   converge to provide a robust estimate of terrestrial amplification,"   
   says Kageyama. "In my view, this strengthens the projections for future   
   climate change, and at the same time brings new understanding of past   
   climate changes."  Funding for this research was provided by a National   
   Science Foundation Division of Earth Sciences award and by the French   
   National Centre for Scientific Research.   
      
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   ==========================================================================   
   Story Source: Materials provided by   
   Woods_Hole_Oceanographic_Institution. Note: Content may be edited for   
   style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Alan M. Seltzer, Pierre-Henri Blard, Steven C. Sherwood, Masa   
      Kageyama.   
      
         Terrestrial amplification of past, present, and future climate   
         change.   
      
         Science Advances, 2023; 9 (6) DOI: 10.1126/sciadv.adf8119   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230208155728.htm   
      
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