Cooperative Institute for Research in Environmental Sciences

An international agreement to deal with ozone-depleting chemicals is working, but newer chemicals contribute to warming

An international agreement in 2007 to deal with the last remaining ozone-depleting chemicals used in large quantities is working, according to a new analysis published today. Atmospheric emissions of those chemicals, called hydrochlorofluorocarbons (HCFCs) and used in refrigeration and air conditioning, are no longer increasing, after having increased consistently over the past few decades, according to NOAA measurements published in the Journal of Physical Chemistry. But the new paper also reports that other substitute chemicals, which are also greenhouse gases, are on the rise, and international decision makers are considering new regulations to cap and reduce those emissions.

“NOAA monitors the composition of Earth's atmosphere closely, and it's that long-term, highly precise monitoring that lets scientists see clear evidence of slowing HCFC emissions since 2007, coincident with the adjustment to the Montreal Protocol,” according to Stephen Montzka, a scientist at NOAA’s Earth System Research Laboratory (ESRL) in Boulder, Colorado, Fellow of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University Colorado Boulder, and the study’s lead author. For more on NOAA’s global sampling network, see sidebar.













NOAA's flask sampling site in the Negev Desert(location WIS on the map of the flask sampling network). NOAA photo.

Last fall, a scientific assessment report for the Montreal Protocol presented further evidence that the international agreement to protect Earth’s ozone layer is working, and that abundances of most ozone-depleting substances in the atmosphere are decreasing. The new paper describes progress in phasing out the last group of ozone-depleters used in significant quantities: HCFCs, which are first-generation replacements for other, more ozone-damaging chemicals initially targeted by the Montreal Protocol.

In 2007, the Montreal Protocol parties agreed to an accelerated schedule for the global phase-out of HCFCs. Although HCFC use in developing countries could have continued until 2040, the prospect that an accelerated phaseout would reduce future ozone depletion and slow climate change in the coming decades prompted the new limits.

This study presents evidence that the recent accelerated phase-out has helped slow global emissions of HCFCs, but it also documented a 45-percent increase in emissions of chemicals used as HCFC substitutes. That’s an important finding, because while these second-generation substitutes, called hydrofluorocarbons, don’t deplete ozone as HCFCs do, many are potent greenhouse gases and contribute to warming, in amounts that are currently small but could become significant in the future.

The study also examined sources of hydrofluorocarbon emissions, finding that global emissions of these chemicals can be attributed in roughly equal amounts to mobile air conditioning, commercial refrigeration, and all other uses (including solvents and industrial refrigeration) combined. This means, says Montzka, that hydrofluorocarbons currently used in car air conditioners contribute substantially to the overall climate impact of this group of chemicals. And while hydrofluorocarbons don’t have a big impact on warming right now, if demand for these chemicals continues to rise, especially in developing countries, those emissions could account for a significant proportion of global greenhouse gases in the future.










Trends in total global emissions of HCFCs and hydrofluorocarbons (HFCs) derived from NOAA's atmospheric measurement network. The graph shows 1) that global emissions of HCFCs (red points) did not increase nearly as fast as they could have in recent years (the red line shows how they might have increased), and 2) that global emissions of hydrofluorocarbons (HFCs, blue points) continue to increase fairly rapidly and consistently, because of their use as substitutes for CFCs and HCFCs throughout the world.

That finding has implications for policy decisions. “We’ve identified how much the different sectors contribute to hydrofluorocarbon emissions,” Montzka says. “This information might help policy makers decide how to reduce emissions more effectively.” For a number of years, parties to the Montreal Protocol have been considering a proposal to cap and reduce hydrofluorocarbons because they contribute to warming.

This paper also shows how policy has influenced atmospheric composition, allowing scientists to see how the 2007 adjustment to the Montreal Protocol, along with other factors, has played out in the atmosphere, says Montzka. David Fahey, director of the Chemical Sciences Division of NOAA’s Earth System Research Laboratory and one of the paper’s co-authors, agreed. “NOAA’s global atmospheric sampling network provides key environmental intelligence that helps inform global policy and determine the effectiveness of policies controlling greenhouse gases and ozone-depleting substances,” says Fahey.

Today’s paper is part a special edition of the Journal of Physical Chemistry dedicated to renowned ozone hole scientist Mario Molina.

This research was made possible as a result of a collaboration between NOAA and CIRES scientists, DuPont Chemicals, and the Institute for Governance and Sustainable Development.

Authors of, “Recent Trends in Global Emissions of Hydrochlorofluorocarbons and Hydrofluorocarbons: Reflecting on the 2007 Adjustments to the Montreal Protocol” are: Stephen Montzka (NOAA and CIRES), Mack McFarland (DuPont Chemicals & Fluoroproducts), Stephen O. Andersen (Institute for Governance & Sustainable Development), Benjamin Miller (CIRES and NOAA), David Fahey (NOAA), Bradley Hall (NOAA), Lei Hu (CIRES and NOAA), Carolina Siso (CIRES and NOAA), and James W. Elkins (NOAA)

CIRES is a partnership of NOAA and CU Boulder.

Storms show a “diverse seasonality,” following seasonal patterns in some regions, but not others

In a state known for its dramatic weather and climate, Colorado’s history of extreme precipitation varies considerably by season and location, according to research published in the current issue of the Journal of Hydrometeorology. Decision makers—often facing increased pressure to consider climate change information—typically turn to historical averages to understand when and where extreme rain, hail and snow happen in this state. But those averages often are not reliable, because they’re based on observations of events that don’t happen frequently and because the observations themselves

are limited, especially in remote areas.

17343656348_6b2721f31f_o.jpgThe climatology of
Colorado’s historical extreme precipitation events shows a remarkable degree of seasonal and regional variability.
 Particularly in the central mountains of Colorado, it’s possible to experience extreme precipitation during any season.

This research set out to improve understanding of the state’s extreme event climatology, because “even in regions where you think you have a strong seasonal signal, the data actually show heavy precipitation events happening outside of the expected time, especially in the central mountains of Colorado,” says Kelly Mahoney, a scientist from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder working at NOAA’s Earth System Research Laboratory (ESRL), and lead author of the new study, which also includes researchers from Scripps Institution of Oceanography at UC San Diego, Colorado State University and the U.S. Geological Survey.

The September 2013 Colorado Front Range floods are evidence that big storms can happen out of season and don’t necessarily obey expected norms. That widespread flooding across northeast Colorado—when the city of Boulder saw just over 17 inches of rain in one week, close to the city’s typical total for the entire year—was unusual in that it happened more than one month after the state’s typical monsoon peak. Though unusual, the floods weren’t unprecedented.

“Because fall is drier on average, the assumption was that we don’t tend to see big precipitation events in the fall. But once these storms happened, people looked back and found other big storms in September, so it’s not that surprising after all,” says Mahoney. Although daily rainfall events in Colorado aren’t as high in September, lots of moisture can still reach the state from both the Gulf of Mexico (because the Atlantic hurricane season is at its peak) and from the Pacific Ocean. According to Mahoney, having a better understanding of the pattern that resulted in the 2013 floods, regardless of the season, could help scientists better anticipate the likelihood of future similar events.



County road in Berthoud, Colorado washed away by the September 2013 Colorado Front Range floods.

credit: Lornay Hansen/CIRES

The precipitation data used in this study came from Cooperative Observer Program (COOP) sites across Colorado. Run by the National Weather Service, COOP relies on volunteers to record daily temperature and precipitation data at sites throughout the United States. The researchers selected precipitation data from the 130 COOP stations throughout Colorado that had a record of at least 30 years of daily data between 1950 and 2010. At each station, the 10 largest daily rain totals were identified and used to characterize Colorado’s extreme precipitation by season.

The researchers found that the largest recorded daily precipitation totals in Colorado vary widely, from about two inches (60 mm) per day in some areas to more than four times that, or about 10 inches (250 mm) per day, in other parts of the state. In general, the heaviest storms tend to happen east of the Continental Divide and in southwestern Colorado, but the seasonality of these big storms isn’t quite so simple.

Across the state, there’s a striking difference when it comes to which seasons see the biggest storms. East of the Continental Divide, most of the largest storms happen in spring, including along Colorado’s Front Range. Farther east still, across the state’s lower-elevation eastern plains, bigger storms are more common in summer. And west of the Continental Divide, at lower elevations, most of the biggest storms happen in fall.

In Colorado’s central mountains, along the spine of the Continental Divide, there’s no clear pattern. The common belief—based on those historical averages—is that winter storms at the state’s highest elevations produce big snow events. That’s not what the researchers found, however. Instead, high-elevation intense precipitation events have occurred in all months of the year, including summer, when that precipitation is more likely to be rain and therefore more of a flood risk.

What’s the take-home message? It’s that Colorado’s extreme precipitation can occur in any season and at all elevations across the state. “Trying to assign extreme events to a certain season is not necessarily a good thing to do, especially here in Colorado,” says Mahoney. Particularly in the central mountains of Colorado, very big storms can happen during any season and it’s important for decision makers to understand that impacts such as flooding are a nearly year-round risk across the state. According to Mahoney, “we need to look at the critical ingredients that come together to produce an extreme event, because that can happen at any time during the year.”

Authors of “Climatology of extreme daily precipitation in Colorado and its diverse spatial and seasonal variability,” are: Kelly Mahoney (CIRES and NOAA), F. Martin Ralph (Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography), Klaus Wolter (CIRES and NOAA), Nolan Doesken (State Climatologist for Colorado and Colorado State University), Michael Dettinger (U.S. Geological Survey and Scripps Institution of Oceanography), Daniel Gottas (NOAA), Timothy Coleman (CIRES and NOAA), and Allen White (NOAA)


CIRES is a partnership of NOAA and CU Boulder.



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