The impact of a future solar minimum on climate change projections in the Northern Hemisphere

Solar variability represents a source of uncertainty in the future forcings used in climate model simulations. Current knowledge indicates that a descent of solar activity into an extended minimum state is a possible scenario. With aid of experiments from a state-of-the-art Earth system model, we investigate the impact of a future solar minimum on Northern Hemisphere climate change projections. This scenario is constructed from recent 11 year solar-cycle minima of the solar spectral irradiance, and is therefore more conservative than the 'grand' minima employed in some previous modeling studies. Despite the small reduction in total solar irradiance (0.36 W m^-2), relatively large responses emerge in the winter Northern Hemisphere, with a reduction in regional-scale projected warming by up to 40%. To identify the origin of the enhanced regional signals, we assess the role of the different mechanisms by performing additional experiments forced only by irradiance changes at different wavelengths of the solar spectrum. We find that a reduction in visible irradiance drives changes in the stationary wave pattern of the North Pacific and sea-ice cover. A decrease in UV irradiance leads to smaller surface signals, although its regional effects are not negligible. These results point to a distinct but additive role of UV and visible irradiance in the Earth's climate, and stress the need to account for solar forcing as a source of uncertainty in regional scale projections.

Simulation of the cold climate event 8200 years ago by meltwater outburst from Lake Agassiz

The cold climate anomaly about 8200 years ago is investigated with CLIMBER-2, a coupled atmosphere-ocean-biosphere model of intermediate complexity. This climate model simulates a cooling of about 3.6 K over the North Atlantic induced by a meltwater pulse from Lake Agassiz routed through the Hudson strait. The meltwater pulse is assumed to have a volume of 1.6 x 10^14 m^3 and a period of discharge of 2 years on the basis of glaciological modeling of the decay of the Laurentide Ice Sheet ( LIS). We present a possible mechanism which can explain the centennial duration of the 8.2 ka cold event. The mechanism is related to the existence of an additional equilibrium climate state with reduced North Atlantic Deep Water (NADW) formation and a southward shift of the NADW formation area. Hints at the additional climate state were obtained from the largely varying duration of the pulse-induced cold episode in response to overlaid random freshwater fluctuations in Monte Carlo simulations. The model equilibrium state was attained by releasing a weak multicentury freshwater flux through the St. Lawrence pathway completed by the meltwater pulse. The existence of such a climate mode appears essential for reproducing climate anomalies in close agreement with paleoclimatic reconstructions of the 8.2 ka event. The results furthermore suggest that the temporal evolution of the cold event was partly a matter of chance.

Incentive based policies on climate change: taxes and tradable emssions permits

The reduction of Greenhouse Gases (GHG) plays a central role in the environmental policies considered by countries for implementation not only at its own level but also at supranational levels. This thesis is dedicated to investigate some aspects of two of the most relevant climate change policies. The first part is dedicated to emission permit markets and the second part to optimal carbon taxes. On emission permit markets we explore the strategic behavior of oligopolistic firms operating in polluting industrial sectors that are regulated by cap and trade systems. Our aim is to identify how market power influences the main results obtained under perfect competition assumptions and to understand how actions taken in one market affects the outcome of the other related market. A partial equilibrium model is developed for this purpose with specific abatement cost functions. In Chapter 2 we use the model to explain some of the most relevant literature results. In Chapter 3 the model is used to analyze different oligopolistic structures in the product market under the assumption of competitive permits market. There are two significant findings. Firstly, under the assumption of a Stackelberg oligopoly, firms have no incentives for lobbying in order to manipulate permit prices up, as they have under Cournot competition...