to below this if climate sensitivity were below 3 °C for doubled . The conclusion was that levels above 450 ppm were considered dangerous, but that reduction in non- greenhouse gases could provide temporary relief from drastic cuts. Further findings are that arctic climate change has been forced by non- constituents as much as by . The 2007 paper cautioned that prompt action is needed to slow growth and to prevent a dangerous anthropogenic interference. Climate model development and projections Vilhelm Bjerknes began the modern development of the general circulation model in the early 20th century. The progress of numerical modeling was slow due to the slow speed of early computers and the lack of adequate observations. It wasn't until the 1950s that the numerical models were getting close to being realistic. Hansen's first contribution to numerical climate models came with the 1974 publication of the GISS model. He and his colleagues claimed that the model was successful in simulating the major features of sea-level pressure and 500mb heights in the North American region. A 1981 Science publication by Hansen and a team of scientists at Goddard concluded that carbon dioxide in the atmosphere would lead to warming sooner than previously predicted. They used a one-dimensional radiative-convective model that calculates temperature as a function of height. They reported that the results from the 1D model are similar to those of the more complex 3D models, and can simulate basic mechanisms and feedbacks. Hansen predicted that temperatures would rise out of the climate noise by the 1990s, much earlier than predicted by other researches. He also predicted that it would be difficult to convince politicians and the public to react. By the early 1980s, the computational speed of computers, along with refinements in climate models, allowed longer experiments. The models now included physics beyond the previous equations, such as convection schemes, diurnal changes, and snow-depth calculations. The advances in computational efficiency, combined with the added physics, meant the GISS model could be run for five years. It was shown that global climate can be simulated reasonably well with a grid-point resolution as coarse as 1000 kilometers. The first climate prediction computed from a general circulation model that was published by Hansen was in 1988, the same year as his well-known Senate testimony. The second generation of the GISS model was used to estimate the change in mean surface temperature based on