LOWELL -- Six-foot snow piles on sidewalks. Local rivers swelling with melted snow and steady March rain. Hurricane Irene. The Halloween snowstorm.
If you remember 2011 as the year of precipitation, that's because it was. Last year was the wettest on record for Lowell since 1893, since the National Oceanic and Atmospheric Association has kept track of climate data in the city, according to the agency's "State of the Climate" report released last month. It was the wettest year for other NOAA monitoring stations in the state, in Ware and West Otis.
Last year's precipitation in Lowell totaled 72.5 inches -- 68 percent more than the normal annual precipitation of 43.1 inches -- topping the previous record of 64.5 inches in 2008. The city also saw 57.5 inches of precipitation in 2010 and 57.37 inches in 2009 while recording 47.8 inches for 2006, the year of the flood that hit some Lowell neighborhoods along the Merrimack River.
In 2011, Massachusetts also saw the warmest fall on record, according to the NOAA.
The Bay State trend was hardly an exception nationally. For the mainland, 2011 was the 23rd warmest on record, with Delaware marking its highest annual temperatures and Texas the second highest. Nationwide, the average annual temperature was 1 degree above the average for the 20th century, according to the report.
Connecticut, New York, New Jersey, Ohio, Pennsylvania, Indiana and Kentucky had their wettest year on record while Texas saw record dryness for the year.
Experts say it's nearly impossible to determine if these weather patterns directly stem from global climate change. That's because weather is driven by tropical day-to-day atmospheric conditions, which are "pretty chaotic," said Juliette Rooney-Varga, associate professor of biological science and director of the Climate Change Initiative at UMass Lowell.
But climate change, which refers to a long-range trend in global weather conditions, provides the baseline for daily weather patterns.
If there is anything to learn from the NOAA's latest report, it's that weather is growing more unpredictable and extreme for this region and elsewhere, said Mathew Barlow, a climate-change expert and professor at UMass Lowell's Environmental, Earth and Atmospheric Sciences Department. That means people can expect to see anything from torrential rain that can result in deadly flash floods to little rain, and heat waves that can bring on drought.
"You need to plan for more crazies," Barlow said.
Global warming promotes extreme weather patterns because it affects the amount of water in the atmosphere, Rooney-Varga said.
According to NOAA, the global average ocean temperature was 72 degrees, above the 20th-century average of 60.9 degrees in 2011, making it the 11th warmest on record. The average land-surface temperature exceeded the 20th-century average of 47.3 degrees by 1.5 degrees, making 2011 the eighth warmest on record. The warmer it gets, the more water evaporates.
Imagine a small bucket and a much larger one, Rooney-Varga said. Warmer air can hold more moisture in it than cooler air does, just as a bigger bucket can hold more water. When it finally reaches a maximum amount and the bucket tips over, a large amount of water suddenly gets dumped at once, whereas less water would fall out of a smaller bucket more frequently. When the air is cooler, it drops smaller amounts of rain more frequently, Rooney-Varga said.
This means cities and towns that have never gone underwater now need to expect floods, extended power outages from storms, prolonged heat waves and many other scenarios. For example, anticipated sea-level rise is projected to cause Boston's 100-year flood plain to far expand from the wharf area into the North End's train-station neighborhood and downtown, depending on how much greenhouse gas that contributes to climate change will be emitted over decades to come, according to the Union of Concerned Scientists.
In Massachusetts, according to a report by UCS, a Cambridge-based nonprofit, spring is arriving earlier, summers are growing hotter and winters are becoming warmer and less snowy. UCS scientists project the Bay State will eventually have a few snow-covered days each winter month, down from the average of one to three weeks, under a high carbon-emissions scenario. Lobsters may also disappear from Massachusetts coastal waters by midcentury due to warmer waters, and cranberries may no longer grow.
To prepare for the consequences of extreme weather events, the Massachusetts Climate Change Adaptation committee, created by the Legislature in 2008, has recommended bolstering the infrastructure. Cross-stream culverts are now designed for higher flood levels, for example, said Tim Purinton, director of Division of Ecological Restoration at the state Department of Fish and Game. The state is also encouraging dam removals, not only to restore natural flows of the rivers but also help prevent floods. One dam removed in Clarksburg a few months before Hurricane Irene last year successfully prevented a flood in that area, Purinton said.
The city of Lowell is moving forward with the plan to separate the sewer lines for stormwater and sewage to prevent overflow of the treatment plant during storms, though the project didn't start out as a climate-mitigation strategy, said City Planner Aaron Clausen.
Climate-change skeptics say the Earth is going through a nominal warming trend as part of a natural phenomenon.
Eric Idso, founder and chairman of the Center for the Study of Carbon Dioxide and Global Change, said in his article published last April 11 on the organization's website that some researchers at the London School of Economics Department of Geography and Environment had found "no significant upward trend in normalized economic losses for either all natural disasters or weather-related disasters."
But whether scientists believe in global warming or not, arctic ice continues to melt. Rooney-Varga said climate change isn't about some obscure "environment." Rather, it's rather about food, water and energy sources that directly affect people's livelihood and safety. The earlier communities start preparing for it, the better off we all will be, Barlow said.