Extreme sensitivity in Snowball Earth formation to mountains on PaleoProterozoic supercontinents

During the PaleoProterozoic 2.45 to 2.2 billion years ago, several glaciations may have produced Snowball Earths. These glacial cycles occurred during large environmental change when atmospheric oxygen was increasing, a supercontinent was assembled from numerous landmasses, and collisions between these landmasses formed mountain ranges. Despite uncertainties in the composition of the atmosphere and reconstruction of the landmasses, paleoclimate model simulations can test the sensitivity of the climate to producing a Snowball Earth. Here we present a series of simulations that vary the atmospheric methane concentration and latitudes of west–east-oriented mountain ranges on an idealised supercontinent. For a given methane concentration, the latitudes of mountains control whether a Snowball Earth forms or not. Significantly, mountains in middle latitudes inhibited Snowball Earth formation, and mountains in low latitudes promoted Snowball Earth formation, with the supercontinent with mountains at ±30° being most conducive to forming a Snowball Earth because of reduced albedo at low latitudes. We propose that the extreme sensitivity of a Snowball Earth to reconstructions of the paleogeography and paleoatmospheric composition may explain the observed glaciations, demonstrating the importance of high-quality reconstructions to improved understanding of this early period in Earth’s history

Predicting plant diversity patterns in Madagascar : understanding the effects of climate and land cover change in a biodiversity hotspot

Climate and land cover change are driving a major reorganization of terrestrial biotic communities in tropical ecosystems. In an effort to understand how biodiversity patterns in the tropics will respond to individual and combined effects of these two drivers of environmental change, we use species distribution models (SDMs) calibrated for recent climate and land cover variables and projected to future scenarios to predict changes in diversity patterns in Madagascar. We collected occurrence records for 828 plant genera and 2186 plant species. We developed three scenarios, (i.e., climate only, land cover only and combined climate-land cover) based on recent and future climate and land cover variables. We used this modelling framework to investigate how the impacts of changes to climate and land cover influenced biodiversity across ecoregions and elevation bands. There were large-scale climate- and land cover-driven changes in plant biodiversity across Madagascar, including both losses and gains in diversity. The sharpest declines in biodiversity were projected for the eastern escarpment and high elevation ecosystems. Sharp declines in diversity were driven by the combined climate-land cover scenarios; however, there were subtle, region-specific differences in model outputs for each scenario, where certain regions experienced relatively higher species loss under climate or land cover only models. We strongly caution that predicted future gains in plant diversity will depend on the development and maintenance of dispersal pathways that connect current and future suitable habitats. The forecast for Madagascar's plant diversity in the face of future environmental change is worrying: regional diversity will continue to decrease in response to the combined effects of climate and land cover change, with habitats such as ericoid thickets and eastern lowland and sub-humid forests particularly vulnerable into the future

Impact of boundary layer processes on seasonal simulation of the East Asian summer monsoon using a Regional Climate Model

In this study, an improved planetary boundary layer (PBL) scheme (YSU scheme) is implemented in a regional climate model (SNURCM) to rectify the systematic bias of the model with the MRF PBL scheme, and the impact of new PBL processes on the simulation of precipitation in the East Asian summer monsoon (EASM) is investigated through regional climate simulations with the MRF and the YSU schemes for the summer of 1998 when extreme floods occurred over East Asia. Compared to the experiment with the MRF scheme that shows excessive monsoon precipitation, particularly over the ocean, the experiment with the YSU scheme improves the seasonal mean precipitation as well as associated large-scale circulations. The temporal progression of the monsoon precipitation and 500hPa geopotential height, and vertical structure are also improved by the revised scheme. The MRF scheme simulates more convective precipitation over the ocean than the YSU scheme, since excessive PBL mixing results in the positive feedback between convective precipitation and latent heat flux at the sea surface. The MRF scheme also simulates more non-convective precipitation over the ocean due to distorted large-scale circulations and excessive PBL mixing. In the experiment with the YSU scheme, the simulated precipitation over the ocean is in good agreement with the observation, since the positive feedback is relatively reduced and large-scale features are reasonably reproduced due to decreased PBL mixing. Excessive PBL mixing in the MRF scheme can also amplify the biases of precipitation over the ocean due to uncoupled air-sea interaction that can result in the imbalance of the energy budget at the sea surface. This implies that new YSU PBL processes can have crucial influences on the regional climate simulation without an ocean model. The results of additional experiments without the spectral nudging technique also reaffirm the impact of the YSU scheme, and further indicate that the development of a coupled regional climate model is required for more reasonable simulation of the EASM.close151

Millennial timescale carbon cycle and climate change in an efficient Earth system model

A new Earth system model, GENIE-1, is presented which comprises a 3-D frictional geostrophic ocean, phosphate-restoring marine biogeochemistry, dynamic and thermodynamic sea-ice, land surface physics and carbon cycling, and a seasonal 2-D energy-moisture balance atmosphere. Three sets of model climate parameters are used to explore the robustness of the results and for traceability to earlier work. The model versions have climate sensitivity of 2.8–3.3°C and predict atmospheric CO2 close to present observations. Six idealized total fossil fuel CO2 emissions scenarios are used to explore a range of 1,100–15,000 GtC total emissions and the effect of rate of emissions. Atmospheric CO2 approaches equilibrium in year 3000 at 420–5,660 ppmv, giving 1.5–12.5°C global warming. The ocean is a robust carbon sink of up to 6.5 GtC year?1. Under ‘business as usual’, the land becomes a carbon source around year 2100 which peaks at up to 2.5 GtC year?1. Soil carbon is lost globally, boreal vegetation generally increases, whilst under extreme forcing, dieback of some tropical and sub-tropical vegetation occurs. Average ocean surface pH drops by up to 1.15 units. A Greenland ice sheet melt threshold of 2.6°C local warming is only briefly exceeded if total emissions are limited to 1,100 GtC, whilst 15,000 GtC emissions cause complete Greenland melt by year 3000, contributing 7 m to sea level rise. Total sea-level rise, including thermal expansion, is 0.4–10 m in year 3000 and ongoing. The Atlantic meridional overturning circulation shuts down in two out of three model versions, but only under extreme emissions including exotic fossil fuel resources