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The North Atlantic-Arctic boundary is highly variable due to the transports of heat and moisture through the Gulf Stream and polar jet stream. The North Atlantic storm track generally follows the Gulf Stream and terminates near southeast Greenland and Iceland as the Icelandic Low. The Icelandic Low is the main driver of the North Atlantic Oscillation, particularly during winter months as the baroclinic zone expands to lower latitudes, correlating with temperature and precipitation in many areas around the North Atlantic. Understanding how atmospheric circulation, temperature, and precipitation changes in this region is important to build robust projections of how these variables will change, especially under natural and anthropogenic forcings. Here, climate proxies correlating to the Icelandic Low, summer air temperature, and annual precipitation build an understanding of how these variables changed over the last 2000 years. Through the natural climate shifts of this period — Roman Warm Period, Dark Ages Cold Period, Medieval Climate Anomaly, and Little Ice Age — it is shown that storm frequency decreases as temperature increases and the Icelandic Low increases in pressure (i.e., becomes weaker). However, these climate changes are not simultaneous, and their amplitudes are not similar across the region. Keeping regionality rather than a pan-Arctic average better explains natural variability of each sub-region and how each sub-region has evolved climatically due to anthropogenic forcings of greenhouse gases.

The surface mass balance of the Greenland ice sheet has decreased in recent decades with important implications for global sea-level rise. Here, a climate reanalysis model is used to examine observed circulation variability and changes in precipitation across southern Greenland to gain insight into the future climate in the region. The influence on precipitation from the North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), Icelandic Low, Azores High, regional blocking patterns, as well as near-surface temperature and winds are explored. Statistically significant correlations are higher between precipitation and the Icelandic Low and near-surface winds (0.5–0.7; p < 0.05) than correlations between precipitation and either the NAO or AMO climate indices (southwest Greenland: r = 0.12 and 0.28, respectively; and southeast Greenland: r = 0.25 and -0.07, respectively). Moreover, the recent enhanced warming in the Arctic (Arctic amplification) and the increase in the Greenland Blocking Index coincide with increased mean annual precipitation and interannual variability in southwest Greenland.

Each student in an introductory college course, Global Climate Change, spends the semester blogging about a country's climate, contribution to global warming through carbon emissions, impacts of climate change, plans to adapt to their changing climate, and attempts to mitigate the problem. Students read and comment on each other's blogs throughout the semester, instilling a global perspective through the use of student-generated content. While the first half of the course focuses on the science of climate change, these blogs supplement course content for the second half of the class and feed class discussions. Students were surveyed before and after the course. When comparing students entering the course to an American population, students were more open minded and more interested in learning about global warming. At the end of the course, students showed significant gains in their knowledge of global warming, but they also gained an increase in perception that people in developing countries woul...

Analysis of the synoptic climatology and precipitation patterns over the North Atlantic region allows for a better understanding of the atmospheric input to the mass balance of the Greenland ice sheet. The self-organizing map (SOM) technique was applied to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) daily sea level pressure (SLP) data from 1961 to 1999 to objectively identify synoptic SLP patterns over the North Atlantic region. A total of 35 different SLP patterns were identified. Patterns common to the winter season are characterized by deep low pressure systems that approach Greenland through an active North Atlantic storm track, whereas patterns most common to the summer months are generally weaker and approach the ice sheet from the west through Baffin Bay. The blocking, splitting, and intensification of cyclones by the high elevations of the Greenland ice sheet were identified in this analysis. Analysis of ERA-40 precipitation associated with each SLP pattern revealed that the largest precipitation events were associated with passing cyclones that created onshore flow, allowing the air to be lifted orographically by the steep margins of the ice sheet. The ERA-40 annual mean precipitation over Greenland from 1961 to 1999 was 35.8 cm yr−1. Greenland was divided into five subregions, and the preferred synoptic patterns for receiving precipitation in each region include cyclones positioned to allow dynamic and orographic lift in each region. Annual precipitation contributions from each SLP pattern were isolated to reveal that half of the annual mean precipitation over Greenland comes from only 11 of the 35 identified synoptic patterns (31.4%), highlighting the importance of studying Greenland precipitation on an event-by-event basis on a daily time scale.

[1] Using a three-model ensemble, predictions of increasing Greenland precipitation over the 21st century are analyzed using self-organizing maps (SOMs). The models that make up the three-model ensemble (CCCMA-CGCM3.1(T63), MIROC3.2(hires), and MPI-ECHAM5), which are all atmosphere-ocean global circulation models used in the Intergovernmental Panel on Climate Change Fourth Assessment Report, were chosen due to their ability to best reproduce North Atlantic surface synoptic climatology and Greenland precipitation from ERA-40. Daily sea level pressure and precipitation data from model simulations for years 1961-1999, 2046-2065, and 2081-2100 are compared, where future simulations are based on the SRES A1B emissions scenario. Results indicate that the North Atlantic storm track is predicted to shift northward through the 21 st century and Greenland precipitation is predicted to increase from 35.8 cm yr -1 to 45.8 cm yr -1 by the end of the 21st century, a 27.8% increase. The precipitation change is attributed to changes in atmospheric circulation, which are due to changes in synoptic pattern frequency of occurrence, and changes in the amount of precipitation that occurs when a given synoptic circulation pattern occurs, termed intrapattern variability, during the future time periods. The northward shift in storm track results in less precipitation being produced dynamically over the southeast coast of Greenland, but an increase in precipitation over the remainder of the ice sheet, with largest increases over the southwest coast of Greenland and the eastern region. Intrapattern variability changes, however, dominate the future precipitation changes, accounting for 82.5% of the total change. This is due to an increase in precipitable water in the atmosphere in response to rising temperatures. Changes in sea ice and ocean temperature are also thought to contribute to this change.

[1] Using the self-organizing map (SOM) technique, the sea level pressure synoptic climatology and precipitation of 15 Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) models are compared to that of the ERA-40 reanalysis for the North Atlantic region for the period 1961 to 1999. Three of the models, the CCCMA-CGCM3.1(T63), the MIROC3.2(hires), and the MPI-ECHAM5, best reproduce the ERA-40 synoptic climatology and are chosen for further analysis of precipitation over Greenland. The MIROC3.2(hires) is the best single performing model, in that it best matches ERA-40. Although the three-model ensemble simulates the same mean annual precipitation over Greenland as ERA-40, the ensemble simulates the mean annual precipitation differently than ERA-40. A dry bias in the CCCMA-CGCM3.1(T63) and a wet bias from the MPI-ECHAM5 cancel in the ensemble average. The mean annual precipitation difference between the model ensemble, as well as each individual model, and ERA-40 is then attributed to differences in intrapattern variability and pattern frequency components in the models that make up the ensemble. Pattern frequency differences between the model and ERA-40 indicate a difference in the occurrence of synoptic weather patterns, while intrapattern variability differences denote differences in the amount of precipitation produced when a given synoptic weather pattern occurs. Intrapattern variability differences between the models and ERA-40 are predominantly responsible for Greenland precipitation differences, but pattern frequency (circulation) differences in the models also play a small role. Part 2 of this paper uses this three-model ensemble to analyze and attribute predicted increases in precipitation over the Greenland ice sheet for the 21st century.