It’s official: 2012 was indeed the hottest year in 100+ years of record keeping for the contiguous U.S. (lower 48 states). The record-breaking heat in March certainly set the table for the record and the heat just kept coming through the summer. The previous record holder is very noteworthy. 2012 broke 1998′s record by more than 1°F! Does that sound small? Let’s put in perspective: that’s the average temperature for thousands of weather stations across a country over 3,000,000 sq. mi. in area for an entire year. Previously to 2012, temperature records were broken by tenths of a degree or so. Additionally, 1998 was the year that a high magnitude El Niño occurred. This El Niño event caused global temperatures to spike to then-record values. The latest La Niña event, by contrast, wrapped up during 2012. La Niñas typically keep global temperatures cooler than they otherwise would be. So this new record is truly astounding!
The official national annual mean temperature: 55.3°F, which was 3.3°F above the 20th century mean value of 52°F.
Figure 1 – NOAA Graph showing year-to-date average US temperatures from 1895-2012.
This first graph shows that January and February started out warmer than usual (top-5), but it was March that separated 2012 from any other year on record. The heat of July also caused the year-to-date average temperature to further separate 2012 from other years. Note the separation between 2012 and the previous five-warmest years on record from March through December. Note further that four of the six warmest years on record occurred since 1999. Only 1921 and 1934 made the top-five before 2012 and now 1921 will drop off that list.
Figure 2 – Contiguous US map showing state-based ranks of 2012 average temperature.
Nineteen states set all-time annual average temperature records. This makes sense since dozens of individual stations set all-time monthly and annual temperature records. Another nine states witnessed their 2nd warmest year on record. Nine more states had top-five warmest years. Only one state (Washington) wasn’t classified as “Much Above Normal” for the entire year. The 2012 heat wave was extensive in space and severe in magnitude.
Usually, dryness tends to accompany La Niña events for the western and central US. This condition was present again in 2012, as the next figure shows.
Figure 3 – Contiguous US map showing state-based ranks of 2012 average precipitation.
As usual, precipitation patterns were more complex than were temperature patterns. Record dryness occurred in Nebraska and Wyoming. Colorado and New Mexico saw bottom-five precipitation years. Severely dry conditions spread across the Midwest all the way to the mid-Atlantic and Georgia continued to experience dryness. Washington and Oregon were wetter than normal as a result of the northerly position of the mean jet stream in 2012. Louisiana and Mississippi saw wetter than normal conditions, largely as a result of Hurricane Isaac.
Figure 4 – Contiguous US map showing state-based average actual precipitation.
I always find it useful to know the magnitude of measurements as well as how they stack up comparatively. Figure 4 provides the former while Figure 3 provides the latter. “Normal” precipitation varies widely across the country and even between neighboring states. How much precipitation fell to allow NE and WY to record driest years on record? 13.04 and 8.03″, respectively. Another useful map would be state-based difference from “normal”.
So the brutal heat that most Americans experienced was one for the record books. As the jet stream remained in a more northerly than usual position, heat across the country dominated. More heat and fewer storm systems in 2012 meant widespread and severe drought expanded across the country. That drought tended to reinforce both the temperatures recorded (drying soils meant incoming solar radiation was more easily converted directly to sensible heat) and the lack of precipitation (dry soils required extra moisture to return to normal conditions).
Thankfully, record-setting temperatures didn’t occur all over the globe in 2012 (although Australia is having their own problems now in 2013). I therefore don’t expect 2012 will be the warmest year on record globally, but a top-10 finish certainly is not out of the question. Again, this is significant because of the extended La Niña event that ended in mid-2012. Without the influence of anthropogenic (man-made) climate change, 2012 probably would have been cooler than will be recorded. The background climate is warming and so La Niñas today are warmer than El Niños of yesterday.
These warming and drying conditions have massive implications for our society. The drought that afflicted the Midwest in 2012 helped push up commodity prices as crops failed. If that trend continues into 2013, prices will rise further, which will pinch all of our finances. Drought in the Southwest and Midwest impacted flows in rivers (Colorado & Mississippi, among others). The former could mean imposed restrictions in 2013 while the latter could mean reduced river transportation, which puts further pressure on goods sold in the US. Conditions aren’t the worst recorded yet, but it is imperative that we examine resource management policies. Are policies robust enough to handle the variability of today’s climate? If not, they probably aren’t equipped to address future variability or change either. What systems are critical to today’s society? If the Southwest remains dry, does agriculture (largest user of CO river water) reduce its use or do urban users? What sets of values guide these and other decision-making processes?