It provides the most detailed picture to date of the impacts on the US in the worst case scenarios, when no action is taken to cut emissions. Examples include: floods in lower Manhattan; a quadrupling of heatwave deaths in Chicago; withering on the vineyards of California; the disappearance of wildflowers from the slopes of the Rockies; the extinction of Alaska’s wild polar bears in the next 75 years.
What lies ahead by region
North-east
The winter snow season could be cut in half in southern New York, Vermont, New Hampshire and Maine — maybe as short as a week or two, under the higher emissions scenario. This would destroy winter traditions like skiing and skating and outdoor ponds. Native cranberries and blueberries would disappear; dairy herds, the biggest agricultural industry, would decline under the higher emissions scenario.
South-east
Summer temperatures in Florida could rise by 4.1C (10.5F), with the heat effect multipled by decreased rainfall under the higher emissions scenario. There would be increased hurricane intensity and rising sea levels leads to loss of wetlands and coastal areas. It would lead to a severe decline in quality of life.
Mid-west
Frequent, severe and longer lasting heatwaves in cities – as many as three a year in Chicago under the higher emissions scenario.
Water levels in the Great Lakes could fall by up to two feet by the end of the century under the higher emissions scenario.
South-west
Continued strong warming will threaten flow of Colorado river.
Alaska
Has been warming at twice the rate of the rest of the US over last 50 years.
Temperatures could rise up to a further 5.4C (13F) under the higher emissions scenario. The region should be prepared for drought and increased risk of wildfire.
North-west
Declining snowpack is already threatening agriculture. Many salmon species are already threatened
Costs
Human health: Rise in deaths due to heatwaves, decline in health because of poor air quality and increase in water borne and insect borne diseases.
Agriculture: Although some crops will benefit from the longer growing season, heavy downpours could wreak havoc on others. Farmers will be forced to use more pesticides and weed killers against invasive plants. Poison ivy will bcome more abundant and more toxic. Higher emissions scenario would cause a 10% decline in dairy herd in Appalachia.
Energy: Rising heat index will increase demand on electricity for air conditioning. But water shortages could restrict electricity generation.
Oil infrastructure, along coast of Louisiana and Florida, is also vulnerable to rising sea levels and intensifying hurricanes.
Transport: Storm surges and rising sea levels could block the use of ports and coastal airports, roads and rail lines. Six of the top 10 freight gateways are threatened by rising sea levels. Entire road networks on the Gulf Coast could be at risk.
Ecosystems: Large-scale shifts in species likely to continue. Deserts will become hotter and drier, oceans more acidic. Salmon and trout populations will contract.
