The Massachusetts Institute of Technology (MIT) Integrated Global System Model is used to make probabilistic projections of climate change from 1861 to 2100. Since the model's first projections were published in 2003, substantial improvements have been made to the model, and improved estimates of the probability distributions of uncertain input parameters have become available. The new projections are considerably warmer than the 2003 projections; for example, the median surface warming in 2091-2100 is 5.18C compared to 2.48C in the earlier study. Many changes contribute to the stronger warming; among the more important ones are taking into account the cooling in the second half of the twentieth century due to volcanic eruptions for input parameter estimation and a more sophisticated method for projecting gross domestic product (GDP) growth, which eliminated many low-emission scenarios.However, if recently published data, suggesting stronger twentieth-century ocean warming, are used to determine the input climate parameters, the median projected warming at the end of the twenty-first century is only 4.18C. Nevertheless, all ensembles of the simulations discussed here produce a much smaller probability of warming less than 2.48C than implied by the lower bound of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) projected likely range for the A1FI scenario, which has forcing very similar to the median projection in this study. The probability distribution for the surface warming produced by this analysis is more symmetric than the distribution assumed by the IPCC because of a different feedback between the

Exposure of plants to ozone inhibits photosynthesis and therefore reduces vegetation production and carbon sequestration. The reduced carbon storage would then require further reductions in fossil fuel emissions to meet a given CO 2 concentration target, thereby increasing the cost of meeting the target. Simulations with the Terrestrial Ecosystem Model (TEM) for the historical period show the largest damages occur in the Southeast and Midwestern regions of the United States, eastern Europe, and eastern China. The largest reductions in carbon storage for the period 1950-1995, 41%, occur in eastern Europe. Scenarios for the 21st century developed with the MIT Integrated Global Systems Model (IGSM) lead to even greater negative effects on carbon storage in the future. In some regions, current land carbon sinks become carbon sources, and this change leads to carbon sequestration decreases of up to 0.4 Pg C yr −1 due to damage in some regional ozone hot spots. With a climate policy, failing to consider the effects of ozone damage on carbon sequestration would raise the global costs over the next century of stabilizing atmospheric concentrations of CO 2 equivalents at 550 ppm by 6 to 21%. Because stabilization at 550 ppm will reduce emission of other gases that cause ozone, these additional benefits are estimated to be between 5 and 25% of the cost of the climate policy. Tropospheric ozone effects on terrestrial ecosystems thus produce a surprisingly large feedback in estimating climate policy costs that, heretofore, has not been included in cost estimates.

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ABSTRACT:A 3-D cloud-resolving model including an explicit aerosol module is used to examine the influence of a range of hygroscopic (CCN) and hydrophobic (IN) aerosol concentrations on the development of a mid-latitude, continental deep convective cloud. The model reproduces a response to changes in CCN which is in agreement with previous studies of continental convection, i.e. lower precipitation rates and a later onset of deep convection for high CCN concentrations. However, the response is non-linear and for low increments of CCN, coalescence and graupel formation becomes more efficient, which increases the total precipitation, i.e. a response similar to what has been obtained for oceanic deep convection. This result indicates the importance of using a range of CCN concentrations when examining aerosol influence on deep convection. The simulations show that an increased IN concentration has a substantial influence on the convective cloud development. Higher IN concentrations generally result in higher updraught velocities, a prolonged precipitation event and larger total precipitation amounts. The radiative forcing exerted by the cloud is determined by the anvil extent and ice crystal size. The anvil area is linked to the average updraught velocity which in turn is found to be correlated with the IN concentration. Homogeneously nucleated ice crystals dominate the total anvil ice mass formed, but heterogeneously formed ice crystals may significantly alter the homogeneous freezing process. For the simulated case, a key parameter for determining whether the number of homogeneously nucleated ice crystals will decrease or increase with increasing IN concentration is the initial updraught velocity. This dependence makes the results sensitive to the amount of heterogeneously formed ice crystals.

[1] We identify and characterize interplanetary coronal mass ejections (ICMEs) observed by Voyager 2 in the heliosphere between 1 and 30 AU. We use abnormally low proton temperatures as the primary identification signature of ICMEs and use other plasma and magnetic field data to verify these identifications. The ICME rate is solar cycle dependent; during the solar minimum of 1986-1987 only a few ICMEs were identified each year, compared with tens per year during solar maxima. The average radial width of ICMEs increases with distance from 1 to $15 AU; outside $15 AU the average radial width is roughly constant. The radial expansion speed of ICMEs is of the order of the Alfvén speed. Comparison of the radial profiles of the ICME and background solar wind shows that the magnetic field decreases faster in ICMEs than in the solar wind but that the density and temperature decrease more slowly than in the solar wind. Many ICMEs identified at Voyager 2 do not have obvious counterparts at Earth. A one-dimensional MHD model is employed to associate ICMEs observed at Earth with those observed at Voyager 2.