Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous

Abstract

We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40 year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change and thus the time scale for paleo global climate, ice sheet, and sea level changes, but this paleo millennial time scale should not be misinterpreted as the time scale for ice sheet response to a rapid large human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6-9 meters with evidence of extreme storms while Earth was less than 1°C warmer than today. Ice melt cooling of the North Atlantic and Southern Oceans, increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2°C global warming above the preindustrial level would be dangerous. Continued high fossil fuel emissions this century are predicted to yield: (1) cooling of the Southern Ocean, especially in the Western Hemisphere, (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss, (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region, (4) increasingly powerful storms, and (5) nonlinearly growing sea IntroductionHumanity is rapidly extracting and burning fossil fuels without full understanding of the consequences. Current assessments place emphasis on practical effects such as increasing extremes of heat waves, droughts, heavy rainfall, floods, and encroach...

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…This caused high sea surface temperatures (Meyers, 2014) and as a global consequence a global increase in evaporation, precipitation and production of brines of higher concentrations. Hansen et al (2016) also pointed out that the increasing meltwater runoff from polar and subpolar ice layers can induce the cover of denser ocean water by a meltwater layer. But the generation of increasing precipitation and surface water runoff accompanied by increasing brine production during hot high-CO 2 climate episodes had exactly the same consequences in the past geological epochs, as we learn from Meyers (2014).…”

“…It is likely that the ratio of organic C burial to carbonate C burial increases greatly during stratified conditions. Concerning the huge fraction of organic C buried during the warm glacial intervals, according to the results of Lopes et al (2015) from the northeast Pa-cific, sediments demonstrate stratification events within the research area of Lopes et al Stratification events may develop by warming the upper water layer, as well as by evaporation and precipitation (Friedrich et al, 2008;Hansen et al, 2016;van Helmond et al, 2015).…”

The effect of model bias on Atlantic freshwater transport and implications for AMOC bi-stability

“…However, several studies suggest that * Corresponding author. e-mail: j.mecking@noc.soton.ac.uk models might be too stable, affecting the likelihood of simulating future abrupt climate change (Valdes, 2011;Drijfhout et al, 2011;Hansen et al, 2016). Projections of the AMOC decline under future climate change have shown a greaterAMOC decrease in CMIP5 models than in CMIP3, suggesting that improvements to climate models may have resulted in an AMOC that is more sensitive to changes in forcing (Reintges et al, 2016).…”

Umwelt und Gesellschaft. Herausforderung für Wissenschaft und Politik

“…(Hansen, et al, 2016 Als dritte Option wird auch diskutiert, in das Klimasystem einzugreifen, indem man gezielt den Strahlungshaushalt der Erde z. B. durch Spiegel oder künstliche Aerosole beeinflusst, oder indem man mit großmaß-stäblichen Methoden Kohlenstoff aus der Atmosphä-re entfernt, etwa durch "Carbon Capture and Storage (CCS)" (NAS 2015a(NAS , 2015b.…”