Human modification of the land surface for farming, water use, housing, infrastructure etc. has a significant impact on global climate. Amongst other land use changes, deforestation results in both biogeochemical and biogeophysical changes. The biogeochemical changes tend to increase temperature by the emission of greenhouse gases such as carbon dioxide and methane. The impacts of biogeophysical changes are many and varied, being dependent on the local climate, soil, and the natural vegetation that is being replaced. There are several mechanisms by which biogeophysical changes due to deforestation can affect the regional climate. A combination of reduction in aerodynamic roughness, in the root extraction of moisture, and in the capture of precipitation on the canopy leads to reduced evaporation and decreases the fluxes of moisture and latent heat from the surface to the atmosphere, which increase the local surface temperature. Conversely, the increase in surface albedo due to deforestation acts to decrease surface temperature by increasing the reflection of shortwave radiation. Understanding how these different factors combine and the sensitivity of climate to changing land use through from prehistory to present and future is important for assessing just how long humans have had a major impact on climate change, and for modelling and attribution of past climate change, as well as providing better assessment of the potential impacts of various policies that involve land use/cover for future climate change mitigation.
Holocene land use and climate change interactions
Episodes of extreme climate variability on interannual to multidecadal time-scales have had major influences on successes and failures of civilizations since the early Holocene (~ 10,000 years). In many cases the magnitude of climate variation in these extreme periods was beyond that seen in the observational record. Historic and pre-historic proxy reconstructions (e.g. tree rings, speleothems etc.) have been primarily used to elucidate regional extreme climate variations and link these to the demise of early civilizations, such as the Akkadian Empire in Mesopotamia or the Maya in Central America. There is debate in the literature about climate impacts versus land degradation and/or socio-political dynamics. However, climate variation is often concluded to be a major factor. In this PhD project we are using global earth system model simulations to examine climate and climate variability over the Holocene to understand (a) how it has varied over the last 10,000 years in key regions of early civilizations as the background climate state has changed, and (b) the degree to which regional human-induced land cover change with the spread of early agriculture influenced climate and climate variability.
Feedbacks between land-use and Atlantic decadal variability: impacts for decadal predictions for Europe
Anthropogenic climate change is predicted to continue over the coming century and beyond. On shorter timescales natural climate variability has a considerable influence on the ability to predict climate change. This variability on inter-annual to multi-decadal scales can overprint anthropogenic changes and can also be affected by them. The need to improve these timescales of climate prediction has been highlighted in the past few years in its importance for government and business planning. The North Atlantic is one region that displays coupled ocean-atmosphere variability, such as the North Atlantic Oscillation. Such variability has an impact on European climate and climate change predictions using climate models. It also influences more idealised climate sensitivity experiments. Understanding this decadal variability, its imprint on regional climate, and its predictability are crucial to constrain uncertainty not just in decadal to centennial climate change predictions, but also for how other sensitivity experiments are undertaken and analysed. Decadal prediction models demonstrate the importance of accurate initialisation of the ocean surface and sub-surface. However, feedbacks between the land surface and ocean decadal variability are an additional important factor that have not thus far been examined to the same degree.
In this PhD project joint with Bristol University, funded by NERC we are using a range of medium to high-resolution climate models from the Hadley Centre (HadCM3 to HadGEM3) in conjunction with observational datasets and IPCC future scenarios (or RCPs: Representative Concentration Pathways). The aim is to investigate the role of recent historical and potential future changes in land-use in modifying N Atlantic decadal ocean variability, and to examine the impacts for decadal climate prediction.
In this PhD project joint with Bristol University, funded by NERC we are using a range of medium to high-resolution climate models from the Hadley Centre (HadCM3 to HadGEM3) in conjunction with observational datasets and IPCC future scenarios (or RCPs: Representative Concentration Pathways). The aim is to investigate the role of recent historical and potential future changes in land-use in modifying N Atlantic decadal ocean variability, and to examine the impacts for decadal climate prediction.
Investigating land cover potential for climate change mitigation
I have been involved in a number of projects from examining how effective future policies might be for regional climate change mitigation in the RCPs (Representative Concentration Pathways) to whether crops can be used to counteract some of the warming we are committed to in the coming decades.
There is increasing certainty that global warming caused by human emissions of carbon dioxide and other greenhouse gases is having a negative impact on the planet. However, despite decades of negotiations and international climate policy it seems unlikely that the emissions targets to avoid dangerous climate change impacts will be met. This has, in the last few years, spurred research into other ways of helping to mitigate for future climate change. One of these is geoengineering (the manipulation of the environment in order to slow or stop the impacts of global climate change). This may be achieved by either reducing concentrations of atmospheric carbon dioxide or increasing the Earth’s reflectivity so that less of the sun’s incoming energy heats the planet. One type of manipulation proposed is crop albedo biogeoengineering, which is the planting of varieties that are more reflective in widespread agricultural crops such as wheat, barley and maize. This has the potential to offset the effect of climate change by causing more of the sun’s energy to be reflected at the Earth’s surface, resulting in cooler temperatures. The initial idea for biogeoengineering originated from work carried out by myself and others at the University of Bristol using computer climate models that demonstrated a regional cooling of over 1 degree C in summer months should be possible. Numerically, this effect may appear small, but in climatological terms, a 1 degree C cooling could have substantial and immediate positive implications on regional weather patterns. Our results also suggested a positive effect on crop productivity in some of these regions. Recent small-scale laboratory experiments on wheat have demonstrated that different varieties do show different levels of reflectivity to light. However, much more extensive studies are needed to survey the full range of wheat varieties, to understand the biological and genetic characteristics that produce variation in reflectivity, and to model the impact on climate using state-of-the-art class Earth system models.
There is increasing certainty that global warming caused by human emissions of carbon dioxide and other greenhouse gases is having a negative impact on the planet. However, despite decades of negotiations and international climate policy it seems unlikely that the emissions targets to avoid dangerous climate change impacts will be met. This has, in the last few years, spurred research into other ways of helping to mitigate for future climate change. One of these is geoengineering (the manipulation of the environment in order to slow or stop the impacts of global climate change). This may be achieved by either reducing concentrations of atmospheric carbon dioxide or increasing the Earth’s reflectivity so that less of the sun’s incoming energy heats the planet. One type of manipulation proposed is crop albedo biogeoengineering, which is the planting of varieties that are more reflective in widespread agricultural crops such as wheat, barley and maize. This has the potential to offset the effect of climate change by causing more of the sun’s energy to be reflected at the Earth’s surface, resulting in cooler temperatures. The initial idea for biogeoengineering originated from work carried out by myself and others at the University of Bristol using computer climate models that demonstrated a regional cooling of over 1 degree C in summer months should be possible. Numerically, this effect may appear small, but in climatological terms, a 1 degree C cooling could have substantial and immediate positive implications on regional weather patterns. Our results also suggested a positive effect on crop productivity in some of these regions. Recent small-scale laboratory experiments on wheat have demonstrated that different varieties do show different levels of reflectivity to light. However, much more extensive studies are needed to survey the full range of wheat varieties, to understand the biological and genetic characteristics that produce variation in reflectivity, and to model the impact on climate using state-of-the-art class Earth system models.