I spent a lot of time on record temperatures in Colorado in 2012 – they were all record highs. Due to annual weather variability, there are a couple of different records in April 2013: record lows. There have been four record lows set or tied in Denver, CO this April:
Needless to say, with record low temperatures due to vigorous synoptic cyclones that brought Arctic air masses down into the middle of the country, April’s average temperature is among the lowest on record. I will have more to say about that next week after the month ends. Denver may not record a bottom-10 moth because much more seasonable weather is on tap for the next week. In contrast, two record highs were set in April 2012: 84F on the 1st and 88F on the 24th.
In other news, Boulder, CO set a monthly record for snowfall: 47.4″ through the 23rd! The old record of 44″ was set in 1957. The official snowfall measurement site for Denver (Denver Int’l Airport) recorded “only” 20.4″ of snow for the month-to-date. With 60F+ temperatures forecasted from today through next Tuesday, DIA won’t challenge the top-10 snowiest Aprils (#10 recorded 21.0″ of snow).
Remember that one month’s, season’s or year’s temperatures, precipitation, or even drought are not indicative by themselves of climate change. They are too heavily influenced by individual weather systems. When I discuss climate change, I write about long-term trends (decadal to multi-decadal). Natural variability influences individual weather events that overlie the long-term climate signal. I’ve written before that climate change means we are more likely to see record high temperatures than record low temperatures. The weather will continue to set both, but will set the former at a higher rate moving forward than the latter. Of course, I for one am very glad there was more precipitation than normal for April. Last year’s drought and record hot summer was not enjoyable to live through. Denver-Boulder and the surrounding region will unfortunately need months in a row of above average precipitation to break the long-term drought. This spring’s precipitation pattern slightly reduced the intensity and areal coverage of drought. I will update my last drought post in the next couple of days.
Through the 20th of December, Denver Colorado’s average temperature measured 7.1°F warmer than average. I told a friend at the time that a monumental shift in weather would have to take place in order for the final month’s tally to approach normal (31.2°F). Well, we got that shift. 7 of the next 11 nights would record lows below 10°F, with the month’s lowest low recorded on the 26th of December (-2°F). 7 of the next 11 days would record highs below 32°F. We started the month on a very different note (Slide 8): four of the first five days saw highs at or above 60°F!
This 2-week period of below-average temperatures was the first such event since February 2012. Every other month this year was characterized by above-average temperatures.
The precipitation deficit continued through December. Denver finished 2012 with 10.11″ of liquid equivalent precipitation, which is 4.19″ below normal.
Average maximum temperature: 68.4°F (+3.7°F above normal)
Average minimum temperature: 39.3°F (+3.0°F above normal)
Mean temperature: 53.9°F (+3.4°F above normal)
73 days above 90°F (33 more than normal; almost double the normal number of 40 days)
19 days with max below 32°F (1 fewer than normal)
132 days with min below 32°F (25 fewer than normal)
Total precipitation: 10.11″ (4.19″ below normal)
Snowfall: 38.5″ (15.3″ below normal)
In summary then, Denver was much warmer and drier than normal in 2012.
2013
Looking ahead, low-frequency climate patterns (e.g. ENSO and IPO) are currently neutral and weakly negative. For the next few months, Denver should see near-average temperatures and near- or below-average precipitation. Since the Denver area is currently experiencing `Moderate` drought conditions, additional below- or near-average precipitation conditions will likely further worsen drought conditions. Any recovery from this drought is likely to be long-term.
This has direct implications on peoples’ lives. Water supply will be strained in early 2013. Agriculture was hit hard by the drought last year and will likely need to plan for continued drought this year. That translates to higher consumer prices for staple goods. Pine forests continue to face stressed environmental conditions (e.g. pine beetle epidemic and drought), setting the stage for another season of terrible forest fires. Stakeholders worked to mitigate some of the climate effects in 2012. They will have to remain vigilant and informed in 2013.
The 2012 U.S. heat wave has made considerable news. So none of this should come as any particular shock, perhaps just a little extra shock to what most of us in the U.S. have experienced so far this year. The average temperature for the contiguous U.S. during June was 71.2°F, which is 2.0°F above the 20th century average, which placed June 2012 as the 12th warmest June on record, as the NCDC announced Monday. June 1933 was the warmest June for the U.S. on record due to Dust Bowl conditions. It was also the tenth driest June on record, even with record precipitation in Florida as a result of Tropical Storm Debby. As I wrote earlier, my state of Colorado experienced its warmest June on record. Seven nearby states experienced top-ten warmest Junes.
The Jan-Jun 2012 period is the warmest such period in U.S. history, as the following graphic displays:
Figure 1. The five warmest years for the contiguous U.S. compared to 2012 as of the end of June 2012.
You can see that the first three months of the year were much warmer than average, but it was March that really pushed conditions to an extreme level: +6F. Since then, the year-to-date average anomaly has edged back down to “just” +4.5F. 1998 was the warmest year on record, largely due to the strong 1997-1998 El Nino event. Note that 2006 also makes this list – and that was without the aid of a strong El Nino. 2012 is clearly much more anomalous than any other year to date. The only way it won’t finish as the warmest year on record is if much cooler than normal conditions blanket most of the country for the remainder of the year. It’s not impossible, but conditions would need to be quite different from what we’ve experienced so far this year.
Meteorologists and climatologists look at other time periods that aren’t calendar years. For instance, the past 12 months (Jul 2011 – Jun 2012) just set a new record for the warmest 12-month period on record in the U.S., squeaking past the record that the end of May (Jun 2011 – May 2012) set, as the following graphic shows:
Figure 2. The set of warmest 12-month periods for the contiguous U.S. in the modern-era.
The past 12 months were 3.23F warmer than the long-term average, which is only slightly higher than the 3.18F anomaly for the preceding 12-month period. These two values are both higher than the 2.83F anomaly for the preceding 12-month period (May 2011-April 2012) and the 2.61F anomaly for April 2011-March 2012. Thus, out of the 12 warmest 12 consecutive month periods in contiguous U.S. history, 1/3 of them have occurred in just over the past year. The odds of this occurring randomly is just 1 in 1,594,323. Thus, until 124,652 AD, we should only see one more 13-month period so warm, and that assumes the climate is staying the same as it did during the past 118 years. Needless to say, such an assumption looks incredibly weak.
Looking further at the graph, you can see that 21st century periods dominate the top-12. That is one important difference from the previous graph which showed 1934 and 1921 and the 3rd and 5th warmest years on record. Those years had stretches of time that were shorter than 12 consecutive months over the entire country that were anomalously warm. The heat that is occurring now is spread over a larger area than previous heat waves. Specific heat values for a location or during just one month might not hit record highs, but overall conditions are warmer now than during previous warm periods in the U.S. In other words, the background climate is warmer than it was in 1921 or 1934, enough so that heat records and long stretches of very warm conditions are a little likelier each year to occur.
Another kind of graph might help the reader visualize this:
The CEI: “summariz[es] and present[s] a complex set of multivariate and multidimensional climate changes in the United States so that the results could be easily understood and used in policy decisions made by nonspecialists in the field.” It shows the percentage area of the U.S. with top 10% extremes. Obviously, January-June 2012 set a new record at 44%.
If the planet continues to warm throughout the 21st century, which is more likely to occur the longer we continue emitting heat-trapping greenhouse gases, months, seasons, and years of time that break records today could be considered cool by comparison to conditions at the end of the century. The implications are wide-ranging and profound for human societies and ecosystems. The world won’t end, but it certainly won’t be the same as today either.
The records really rolled in last week throughout the eastern US. Daily temperature records are normally broken by a degree or two at stations that have existed for 100 years or so. What made last week special? Daily record temperature maxima were broken by 20, 30, even 40 degrees F – at stations that have existed for a long time! These types of events simply do not happen given the length of temperature data already in the books. The geographical extent, magnitude of anomalous warmth and temporal occurrence was simply stunning from a scientific viewpoint.
Put simply, it is extremely unlikely that this event could have happened without the base climate warming beforehand. As the globe continues to warm, these type of events will unfortunately become a little more common. As I and others have explained before, the greatest effects of global warming won’t necessarily be felt first by those who live closer to the Equator. Instead, it is the higher latitudes that will warm more quickly – which will have the effect of extending the yearly warm season to earlier and later dates in a calendar year. So winters and higher latitudes will be affected first – just as we’ve seen to date.
To end on a somewhat foreboding note, keep in mind that this warming is the physical response to greenhouse gas emissions of ~30 years ago. We won’t see the results of the additional emissions throughout those 30 years for another generation. The need for decisive action on mitigation and adaptation grows daily.
