365 Days of Climate Awareness 159 – 2013 State of the Climate, North America

2013 US Climate Data

• Global atmospheric CO₂ concentration: 395.4ppm, +2.75 ppm from 2012
• Average air temperature: 54.4°F, 40^th all-time 1895-2021
• Average precipitation: 28.85”, 34^th wettest (94^th driest) 1895-2021
• Tornadoes: 906, 347 (28%) below the ten-year average 1253
• 13 named tropical cyclones: 2 hurricanes, 0 major (winds > 111 mph, 3-5 Saffir-Simpson)
• Atlantic ACE: 38.92 x 10⁴ kts²
• ENSO: Neutral

Larger Version

North American Conditions

• Warmer than average: Canada; northeastern and western US; Mexico
• Cooler than average: Midwest, Great Plains, and southeastern US;
• Drier than average: Canada; US west of the Rockies; Mexico
• Wetter than average: US east of the Rockies
• Wildfires: Below-average wildfire activity
• Snow cover: above average winter and spring

2013 was an extremely light year for tornado and Atlantic cyclone activity. Generally neutral or negative (La Niña) ENSO states lead to reduced wind shear in the tropical Atlantic, which favors the development of the strong vertical convection currents central to cyclones. This appears to be due to low sea surface temperatures in the eastern tropical Atlantic, part of what is called the Main Development Region (MDR), which interfered with the atmospheric pressure patterns and inhibited cyclone development. 

Predictions had been for a very active hurricane season so this effect caught meteorologists (pleasantly) by surprise, but might be connected to some more ominous trends. The anomalously cool eastern MDR seems to be connected to a weaker-than-usual Atlantic Meridional Overturning Circulation (AMOC)—the North Atlantic thermohaline current system.

2013 US Percentage Area Very Warm vs Very Cold (top 10th percentile for each)

The Arctic Ocean is acidifying as well as warming. Arctic amplification—the tendency for added heat energy in the climate system to migrate to the high northern latitudes—has opened a number of pathways for added CO₂ uptake there. The two largest are direct absorption from the atmosphere, increased in recent years due to declining ice cover. The second is the influx of Pacific water through the Bering Strait, which has increasing CO₂ concentrations. The warming and the acidification of the Arctic Ocean are combining to fundamentally change the ecosystem there, from primary production up to apex predators.

2013 US Percentage Area Very Wet vs Very Dry (top 10th percentile for each)

Tomorrow: 2013 State of the World Climate.

Be brave, and be well. Now is not the time to lose hope.