bluewave

Tree and shrub growth in Central Park really began to block the sun from reaching the sensor around 1991. From 1931 to 1991, NYC was generally -2 to +2 warmer than Newark. This was before the deep shade during the peak daily heating hours at the NYC ASOS. Since 1991, NYC has been about -2 to -4 cooler than Newark for the years that went to 100° or greater at Newark. So it’s quite possible that the trees being too close in 2011 prevented NYC from making a run at the 1936 all-time record. Years with a Tie and NYC in the lead bolded Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Jan through Dec Click column heading to sort ascending, click again to sort descending. Rank Year Highest Max Temperature NYC Max Temperature 1 2011 108 104….-4 2 2001 105 103….-2 - 1993 105 102….-3 - 1966 105 103….-2 - 1953 105 102….-3 - 1949 105 102….-3 3 2012 104 100…-4 - 1995 104 102….-2 - 1936 104 106…+2 4 2021 103 98….-5 - 2010 103 outage missed high 103……? - 1999 103 101….-2 - 1954 103 100….-3 - 1948 103 103…..T 5 2005 102 99….-3 - 1994 102 98….-4 - 1991 102 102….T - 1977 102 104.+2 - 1952 102 100…-2 - 1944 102 102...T - 1943 102 99…-3 6 2013 101 98….-3 - 2006 101 97….-4 - 1997 101 97….-4 - 1988 101 99…-2 - 1980 101 102…+1 - 1957 101 101…..T - 1955 101 100….-1 - 1933 101 102….+1 7 2002 100 98….-2 - 1986 100 98….-2 - 1982 100 98….-2 - 1973 100 98….-2 - 1963 100 98…-2 - 1959 100 97…-3 - 1937 100 100…T - 1934 100 101….+1

The 99th percentile event, by definition, occurs 1 day in 100. Since there are 92 days in the Jun-Aug period, it is approximately a 1 year event. 2/ Because temperatures are recorded in whole degrees °F and the differences are typically in the small single digits, the map has a somewhat mottled appearance. 3/ If you remove "major" big city stations, the map looks almost identical and the gridded average only changes by 0.06°F. 4/ Finally, what about all that blue??? It's well understood that decades of land use and irrigation changes in the Great Plains has led to less extreme summer temperatures over the decades. This is, quite literally, a human induced change of the climate. 5/5

We are on track for the first two Julys in a row with a tropical storm around the 9th-10th. Area Forecast Discussion National Weather Service New York NY 232 PM EDT Fri Jul 10 2020 .SYNOPSIS... Tropical Storm Fay will move northward along the Mid Atlantic coast today Latest EPS Elsa forecast

Plenty of smoke from the wildfires.

The June heat this year was very unusual on several fronts. The all-time heat records in the West occurred in June instead of July. All-time heat records are usually set in July. The Newark 103° at the end of June and 597 dm ridge were also early. So we’ll have to see if this means a rare June highest temperature. The active convection pattern coming up also feels like what we see sometimes in August after late July hottest temperatures of the summer.

The latest EPS weeklies have an active storm track the next few weeks. So it’s possible that the 103°at Newark last week won’t get surpassed for a while. Sometimes it can be tough to rival a heatwave once a pattern becomes wetter. July 5-12 July 12-19

Yeah, the corn has kept the Plains cooler than the East and West. https://www.sciencemag.org/news/2018/02/america-s-corn-belt-making-its-own-weather The United States’s Corn Belt is making its own weather By Kimberly HickokFeb. 16, 2018 , 12:05 PM The Great Plains of the central United States—the Corn Belt—is one of the most fertile regions on Earth, producing more than 10 billion bushels of corn each year. It’s also home to some mysterious weather: Whereas the rest of the world has warmed, the region’s summer temperatures have dropped as much as a full degree Celsius, and rainfall has increased up to 35%, the largest spike anywhere in the world. The culprit, according to a new study, isn’t greenhouse gas emissions or sea surface temperature—it’s the corn itself. This is the first time anyone has examined regional climate change in the central United States by directly comparing the influence of greenhouse gas emissions to agriculture, says Nathan Mueller, an earth systems scientist at the University of California (UC), Irvine, who was not involved with this study. It’s important to understand how agricultural activity can have “surprisingly strong” impacts on climate change, he says. The Corn Belt stretches from the panhandle of Texas up to North Dakota and east to Ohio. The amount of corn harvested in this region annually has increased by 400% since 1950, from 2 billion to 10 billion bushels. Iowa leads the country for the most corn produced per state. To see whether this increase in crops has influenced the region’s unusual weather, researchers at the Massachusetts Institute of Technology in Cambridge used computers to model five different 30-year climate simulations, based on data from 1982 to 2011. First, they compared simulations with high levels of intense agriculture to control simulations with no agricultural influence. Unlike the real-life climate changes, the control simulations showed no change in temperature or rainfall. But 62% of the simulations with intense agriculture resulted in temperature and rainfall changes that mirror the observed changes, the team reports this week in Geophysical Research Letters. Map of the central United States, showing changes in rainfall during the last third of the 20th century. Areas of increased rainfall are shown in green, with darker colors representing a greater increase. MASSACHUSETTS INSTITUTE OF TECHNOLOGY The team then compared its results to historical global simulations from the World Climate Research Programme (WCRP), an international program for the coordination of global climate research sponsored by the International Council for Science, the World Meteorological Organization, and the Intergovernmental Oceanographic Commission of UNESCO. WCRP’s models take into account greenhouse gas emissions and other natural and humanmade influences, but do not consider agricultural land use. When researchers ran the numbers for the Corn Belt, the global models fell short of reality: They predicted both temperature and humidity to increase slightly, and rainfall to increase by up to 4%—none of which matches the observed changes. Other climate simulations that use sea surface temperature variation didn’t match observed changes, either. Those simulations matched historical data until 1970; after that, the simulations predicted temperatures to keep increasing, rather than decreasing as they did in reality. This is a strong indication that agriculture, and not changing sea surface temperature, caused the regional changes in climate during the last third of the 20th century, the researchers say. “The [influence] of agriculture intensification is really an independent problem from greenhouse gas emissions,” says Ross Alter, lead author of the study and now a meteorologist with the U.S. Army Corps of Engineers in Hanover, New Hampshire. In fact, Alter says, heavy agriculture likely counteracted rising temperatures regionally that might have otherwise resulted from increasing greenhouse gas emissions. One other place that shows a similar drop in temperatures, he notes, is eastern China, where intensive agriculture is widespread. But how does agriculture cause increased rainfall and decreased temperatures? The team suspects it has to do with photosynthesis, which leads to more water vapor in the air. When a plant’s pores, called stomata, open to allow carbon dioxide to enter, they simultaneously allow water to escape. This increases the amount of water going into the atmosphere and returning as rainfall. The cycle may continue as that rainwater eventually moves back into the atmosphere and causes more rainfall downwind from the original agricultural area. Rong Fu, a climate scientist at UC Los Angeles, agrees with the team’s assessment. She also thinks that though human influence might be “greater than we realize,” this regional climate change is probably caused by many factors, including increased irrigation in the region. “This squares with a lot of other evidence,” says Peter Huybers, a climate scientist at Harvard University, who calls the new study convincing. But he warns that such benefits may not last if greenhouse gas emissions eventually overpower the mitigating effect of agriculture. Alter agrees, and says it’s unlikely that the large increases in U.S. crop production during the 20th century will continue. Other scientists have voiced concern that agricultural production could soon be reaching its limit in many parts of the world. “Food production is arguably what we’re more concerned about with climate change,” Mueller says. And understanding how agriculture and climate will continue to affect one another is crucial for developing projections for both climate and agricultural yields. “It’s not just greenhouse gasses that we need to be thinking about.”

The Euro has more +20 C 850 mb temps Tuesday and Wednesday. It will be interesting to see if the smoke is thick enough to prevent more 100° readings. Tough to tell how much if any influence it will have on our temperatures.

https://xmacis.rcc-acis.org

Recent studies have identified +2 C of global warming as a critical threshold for the Arctic and Antarctic. https://www.nature.com/articles/s41558-018-0127-8?WT.feed_name=subjects_climate-and-earth-system-modelling Arctic sea ice has declined rapidly with increasing global temperatures. However, it is largely unknown how Arctic summer sea-ice impacts would vary under the 1.5 °C Paris target compared to scenarios with greater warming. Using the Community Earth System Model, I show that constraining warming to 1.5 °C rather than 2.0 °C reduces the probability of any summer ice-free conditions by 2100 from 100% to 30%. It also reduces the late-century probability of an ice cover below the 2012 record minimum from 98% to 55%. For warming above 2 °C, frequent ice-free conditions can be expected, potentially for several months per year. Although sea-ice loss is generally reversible for decreasing temperatures, sea ice will only recover to current conditions if atmospheric CO2 is reduced below present-day concentrations. Due to model biases, these results provide a lower bound on summer sea-ice impacts, but clearly demonstrate the benefits of constraining warming to 1.5 °C. https://theconversation.com/antarctica-is-headed-for-a-climate-tipping-point-by-2060-with-catastrophic-melting-if-carbon-emissions-arent-cut-quickly-160978 The new study shows that if emissions continue at their current pace, by about 2060 the Antarctic ice sheet will have crossed a critical threshold and committed the world to sea level rise that is not reversible on human timescales. Pulling carbon dioxide out of the air at that point won’t stop the ice loss, it shows, and by 2100, sea level could be rising more than 10 times faster than today. The tipping point Antarctica has several protective ice shelves that fan out into the ocean ahead of the continent’s constantly flowing glaciers, slowing the land-based glaciers’ flow to the sea. But those shelves can thin and break up as warmer water moves in under them. As ice shelves break up, that can expose towering ice cliffs that may not be able to stand on their own. There are two potential instabilities at this point. Parts of the Antarctic ice sheet are grounded below sea level on bedrock that slopes inward toward the center of the continent, so warming ocean water can eat around their lower edges, destabilizing them and causing them to retreat downslope rapidly. Above the water, surface melting and rain can open fractures in the ice. When the ice cliffs get too tall to support themselves, they can collapse catastrophically, accelerating the rate of ice flow to the ocean. The study used computer modeling based on the physics of ice sheets and found that above 2 C (3.6 F) of warming, Antarctica will see a sharp jump in ice loss, triggered by the rapid loss of ice through the massive Thwaites Glacier. This glacier drains an area the size of Florida or Britain and is the focus of intense study by U.S. and U.K. scientists. To put this in context, the planet is on track to exceed 2 C warming under countries’ current policies. Other projections don’t account for ice cliff instability and generally arrive at lower estimates for the rate of sea level rise. While much of the press coverage that followed the new paper’s release focused on differences between these two approaches, both reach the same fundamental conclusions: The magnitude of sea level rise can be drastically reduced by meeting the Paris Agreement targets, and physical instabilities in the Antarctic ice sheet can lead to rapid acceleration in sea level rise. The disaster doesn’t stop in 2100 The new study, led by Robert DeConto, David Pollard and Richard Alley, is one of the few that looks beyond this century. One of us is a co-author. It shows that if today’s high emissions continued unabated through 2100, sea level rise would explode, exceeding 2.3 inches (6 cm) per year by 2150. By 2300, sea level would be 10 times higher than it is expected to be if countries meet the Paris Agreement goals. A warmer and softer ice sheet and a warming ocean holding its heat for centuries all prevent refreezing of Antarctica’s protective ice shelves, leading to a very different world.

In the opposite direction, this was the 5th coolest July daily maximum temperature at LGA. None of the top 5 had a 100° day occurrence near the date. The closest would be 1941 but it came up just short. Almanac for LAGUARDIA AIRPORT, NY June 30, 2021 Daily Data Observed Normal Record Highest Record Lowest Max Temperature 100 85 100 in 2021 66 in 1967 Almanac for LAGUARDIA AIRPORT, NY July 3, 2021 Daily Data Observed Normal Record Highest Record Lowest Max Temperature 67 86 107 in 1966 67 in 2021 Time Series Summary for LAGUARDIA AIRPORT, NY - Month of Jul Click column heading to sort ascending, click again to sort descending. Rank Year Lowest Max Temperature Min Max Dates 1 1978 62 7-4…62…7-6….85 - 1956 62 7-6….62…7-2…94 2 1941 64 7-4….64…7-2…98 3 1972 65 7-5…65…7-2….72 - 1964 65 7-9….65….7-1….97 4 2005 66 7-8….66…7-11….92 5 2021 67 6-30…100….7-3…67 - 1961 67 7-15….67…7-18…89

This was the first time ever that LGA had a high in the 60s only three days after reaching 100°. I will just add the instances of late June and July 100s below. The high of 67° yesterday was well below the average following so soon after a 100° day. 6-30-21….100 7-3-21……67 6-26-52….101 6-28-52……82 7-21-19…..100 7-22-19…..77 7-19-13….100 7-22-13….82 7-18-12…..101 7-20-12……73 7-6-10…..103 7-7-10…..101 7-10-10….85 7-27-05….100 7-28-05….81 7-6-99…..101 7-9-99……85 7-15-95….103 7-16-95…..86 7-20-91…..101 7-21-91…..100 7-22-91……89 7-2-66….101 7-3-66….107 7-6-66….87 7-22-57….101 7-23-57…82 7-22-55….100 7-23-55….100 7-24-55….87

This was the warmest June on record from the Pacific Northwest across Canada to New England and the Canadian Maritimes. The most extreme heat was closest to the areas of the greatest 500 mb height long term height increases over Western North America. Those areas experienced all-time 500 mb heights near 600 dm. The secondary area of record warmth was located closer to New England where a June record 597 mb height was recorded at Upton, NY. This is the other region with fastest rising long term 500 mb heights east of New England.

Probably the first year that a Memorial Day weekend and July 4th weekend had at least one day with such a cool max. All the more unusual when you consider that we had record heat before both weekends. Goes to the extreme wavelength changes that we have been experiencing over short periods of time.

It will be easier for LGA since it’s closer to the UL and has a cool NE flow off the Sound. Data for December 25 - LAGUARDIA AIRPORT, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature July 3rd Max Temperature 2015-12-25 64 82 0.0 0 2020-12-25 63 ? 0.0 0 2014-12-25 63 81 0.0 0 1982-12-25 62 91 0.0 0 1940-12-25 60 91 0.0 0

This new winter negative feedback may be another reason why the 2012 record has held on. It is important to stress that in the above analysis we are discussing winter ice growth, not the end of winter thickness https://www.nasa.gov/feature/goddard/2018/wintertime-arctic-sea-ice-growth-slows-long-term-decline-nasa New NASA research has found that increases in the rate at which Arctic sea ice grows in the winter may have partially slowed down the decline of the Arctic sea ice cover. As temperatures in the Arctic have warmed at double the pace of the rest of the planet, the expanse of frozen seawater that blankets the Arctic Ocean and neighboring seas has shrunk and thinned over the past three decades. The end-of-summer Arctic sea ice extent has almost halved since the early 1980s. A recent NASA study found that since 1958, the Arctic sea ice cover has lost on average around two-thirds of its thickness and now 70 percent of the sea ice cap is made of seasonal ice, or ice that forms and melts within a single year. But at the same time that sea ice is vanishing quicker than it has ever been observed in the satellite record, it is also thickening at a faster rate during winter. This increase in growth rate might last for decades, a new study accepted for publication in Geophysical Research Letters found. This does not mean that the ice cover is recovering, though. Just delaying its demise. "This increase in the amount of sea ice growing in winter doesn’t overcome the large increase in melting we've observed in recent decades," said Alek Petty, a sea ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study. "Overall, thickness is decreasing. Arctic sea ice is still very much in decline across all seasons and is projected to continue its decline over the coming decades. " Petty and his team used climate models and observations of sea ice thickness from the European Space Agency’s CryoSat-2 satellite to explore sea ice growth variability across the Arctic. The climate model results compared well both with CryoSat-2’s measurements and the results of another commonly used Arctic sea ice model, giving the authors confidence in the climate model’s ability to capture Arctic sea ice variability. "The global climate model seems to do a good job of capturing the Arctic sea ice state and shows that most of the thickness change in the central Arctic is from thermodynamics, that is, ice formation and ice melt, although around the Arctic sea ice edge dynamics, which is ice transport, can play a bigger role," Petty said. These model simulations showed that in the 1980s, when Arctic sea ice was on average 6.6 feet thick in October, about 3.3 extra feet of ice would form over the winter. That rate of growth has increased and may continue to do so for several more decades in some regions of the Arctic; in the coming decades, we could have an ice pack that would on average be only around 3.3 feet thick in October, but could experience up to 5 feet of ice growth over the winter. It seems counterintuitive: how does a weakening ice cover manage to grow at a faster rate during the winter than it did when the Arctic was colder and the ice was thicker and stronger? "Our findings highlight some resilience of the Arctic sea ice cover," Petty said. "If we didn't have this negative feedback, the ice would be declining even faster than it currently is. Unfortunately, the positive feedback loop of summer ice melt and increased solar absorption associated with summer ice melting still appears to be dominant and continue to drive overall sea ice declines." Nonetheless, the increased rate of sea ice thickening in winter has other implications. As ice forms at the ocean surface, it releases a lot of the salty and dense water from which it originated, which sinks and increases the mixing of waters in the upper ocean. The more ice formation that takes place, the more mixing we expect to see in the upper ocean. Increases in this ice formation and mixing during winter may help mitigate the strong freshening of the Arctic Ocean’s surface waters that has been observed in recent decades due to increased summer melt. "This is altering the seasonal balance and the salinity distribution of the upper ocean in the Arctic; it's changing when we have fresh water, when we have salty water and how deep and seasonal that upper oceanic mixed layer is," Petty said. "And that's all going to mean that local micro-organisms and ecosystems have to adapt to these rapidly evolving conditions." Petty’s projections found that, by the middle of the century, the strong increases in atmospheric and oceanic temperatures will outweigh the mechanism that allows ice to regrow faster, and the Arctic sea ice cover will decline further. The study predicted that the switch will happen once the sea ice is less than 1.6 feet thick at the beginning of winter, or its concentration –the percentage of an area that is covered in sea ice– is less than 50 percent. "This negative feedback mechanism increasing ice growth is unlikely to be sufficient in preventing an ice-free Arctic this century," Petty and his colleagues concluded. Petty’s study was carried out in collaboration with scientists from the National Center for Atmospheric Research in Boulder, Colorado, with additional funding provided by the National Science Foundation's Office of Polar Programs For more information: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL079223

I know that the obvious focus of this extreme event was the all-time nature of the heat for any month by such a wide margin. But the other story is how many stations across the country set or tied their June monthly high temperature from the Pacific NW across to New England. It’s very unusual to set or tie all-time record highs for a month from the NW to the NE in the same month. This may have been the first time that Portland Maine and Portland Oregon had a warmest month at the same time. Time Series Summary for Portland Area, ME (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 2021 68.9 0 2 2001 67.1 0 3 1884 67.0 0 Time Series Summary for Portland Area, OR (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 2021 70.7 0 2 2015 70.3 0 3 1992 67.4 0 New June maximum temperature records Click column heading to sort ascending, click again to sort descending. Rank Year Highest Max Temperature Missing Count - - - Time Series Summary for Boston Area, MA (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Max Temperature Missing Count 1 2021 100 0 - 1952 100 0 - 1925 100 0 Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Max Temperature Missing Count 1 2021 103 0 2 2011 102 0 - 1994 102 0 - 1993 102 0 - 1952 102 0 - 1943 102 0 Time Series Summary for Missoula Area, MT (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Max Temperature Missing Count 1 2021 102 0 - 2015 102 0 3 1937 100 0 Time Series Summary for Salt Lake City Area, UT (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Max Temperature Missing Count 1 2021 107 0 2 2013 105 0 3 2015 104 0 - 1979 104 0 - 1961 104 0 Time Series Summary for Grand Junction Area, CO (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Max Temperature Missing Count 1 2021 105 0 - 1990 105 0 2 2016 104 0 - 1994 104 0 - 1900 104 0 All-time June monthly warmest minimum temperatures Time Series Summary for Caribou Area, ME (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Min Temperature Missing Count 1 2021 69 0 - 2017 69 0 - 1949 69 0 - 1942 69 0 Time Series Summary for Portland Area, ME (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Min Temperature Missing Count 1 2021 75 0 2 1931 74 0 - 1923 74 0 - 1901 74 0 Time Series Summary for Syracuse Area, NY (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Min Temperature Missing Count 1 2021 78 0 2 1999 77 0 3 1925 76 0 Time Series Summary for Concord Area, NH (ThreadEx) - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Min Temperature Missing Count 1 2021 74 0 - 1875 74 0 Time Series Summary for WESTCHESTER CO AP, NY - Month of Jun Click column heading to sort ascending, click again to sort descending. Rank Year Highest Min Temperature Missing Count 1 2021 77 0 - 1991 77 2

https://yaleclimateconnections.org/2021/07/western-canada-burns-and-deaths-mount-after-worlds-most-extreme-heat-wave-in-modern-history/ This is the most anomalous regional extreme heat event to occur anywhere on Earth since temperature records began. Nothing can compare,” said weather historian Christopher Burt, author of the book “Extreme Weather.” Pointing to Lytton, Canada, he added, “There has never been a national heat record in a country with an extensive period of record and a multitude of observation sites that was beaten by 7°F to 8°F.” International weather records researcher Maximiliano Herrera (@extremetemps) agrees. “What we are seeing now is totally unprecedented worldwide,” said Herrera, who tweeted on June 30, “It’s an endless waterfall of records being smashed.” Some examples of the extremity of this event, based on preliminary data: • Portland, Oregon, broke its longstanding all-time record high (107°F from 1965 and 1981) on three days in a row – a stunning feat for any all-time record – with highs of 108°F on Saturday, June 26; 112°F on Sunday; and 116°F on Monday. That 116°F is one degree higher than the average daily high on June 28 at Death Valley, California. • Quillayute, Washington, broke its official all-time high by a truly astonishing 11°F, after hitting 110°F on Monday (old record: 99°F on August 9, 1981). Quillayute is located near the lush Hoh Rain Forest on the Olympic Peninsula, just three miles from the Pacific Ocean, and receives an average of 100 inches of precipitation per year. • Jasper, Alberta, broke its all-time high of 36.7°C (98.1°F) on four days in a row, June 27-30, with highs of 37.3°C, 39.0°C, 40.3°C, and 41.1°C (99.1°F, 102.2°F, 104.5°F, and 106°F). • All-time state highs were tied in Washington (118°F at Dallesport) and set in Oregon (118°F at Hermiston, beating the reliable record of 117°F), and provincial highs were smashed in British Columbia (49.6°C at Lytton, beating 39.1°C) and Northwest Territories (39.9°C at Fort Smith, beating 31.7°C). According to Herrera, more all-time heat records have been broken by at least 5°C (9°F) in the past week’s heat wave than in the previous 84-plus years of world weather recordkeeping, going back to July 1936. It’s worth noting that the record North American heat of the 1930s, including 1936, was largely connected to the Dust Bowl, in which the effects of a multiyear drought were amplified by over-plowed, denuded soil across the Great Plains – an example of human-induced climate change itself, albeit temporary. Preliminary data from NOAA’s U.S. Records website shows that 55 U.S. stations had the highest temperatures in their history in the week ending June 28. More than 400 daily record highs were set. Over the past year, the nation has experienced about 38,000 daily record highs versus about 18,500 record lows, consistent with the 2:1 ratio of hot to cold records set in recent years.

https://theconversation.com/why-arctic-melting-will-be-erratic-in-the-short-term-35969 Why Arctic melting will be erratic in the short term Arctic sea ice melts each summer, reaching its minimum extent sometime in September, before refreezing through the winter. Over the past 35 years, the September sea ice extent has reduced by about 35% overall and this decline is projected to continue as global temperatures increase. In 2007 and 2012 the summer ice extent was dramatically lower, causing some some media speculation that we would soon see a summer which was “ice-free” (meaning a year with less than 1 million km2 of sea-ice). Most climate scientists were more cautious. The weather in 2007 and 2012 was warmer than usual and the winds were particularly favourable for melting sea ice. Although human influence on Arctic sea ice has been detected, there was no evidence that these weather patterns would continue each year. In contrast, 2013 and 2014 had more sea ice than 2012, causing other speculation that a recovery was underway. Is this claim warranted? The figure below shows Arctic sea ice extent (the black line) has undergone a long-term decrease, with the dashed line representing a linear trend. But there have also been shorter periods of rapid melt, no change, and apparent increases in extent during this decline – represented below by coloured trend lines for some deliberately chosen eight year periods. Satellite observations of September Arctic sea ice extent. Ed Hawkins/University of Reading The most recent eight-year period, starting from the extreme low of 2007, shows an upward trend. This does not mean that the Arctic sea ice is recovering. As with global temperature, these erratic changes are what we expect to see. Bouncing towards an ice-free summer Imagine a ball bouncing down a bumpy hill. Gravity will ensure that the ball will move downwards. But if the ball hits a bump at a certain angle it might move horizontally or even upwards for a time, before resuming its inevitable downward trajectory. This bouncing ball is an analogy for the changing Arctic sea ice. The hill represents the long-term downward trend in Arctic sea ice due to increasing global temperatures and the bumps introduce changes from this smooth trajectory. These erratic bounces could be in either direction, causing an apparent acceleration or temporary reduction in melt rate. By only examining a small part of the trajectory you might conclude that the ball was moving against gravity. A longer term view would see it as a bounce. There is no expectation that sea ice, or any other aspect of the climate, will change smoothly over time. The climate system simply does not work that way. Previous studies have suggestedthat natural climate variations (or “bounces”) play a key role in how sea ice evolves, and suggested that some of the rapid melt in the early 2000s was a temporary acceleration. A new study I co-authored with a team of Canadian and American scientists, published in Nature Climate Change, highlights that the recent slower melt is a temporary, but not unexpected, deceleration. The complex climate models used to make projections of future climate also exhibit similar periods of little change and more rapid change in Arctic sea ice. The recent trends are well within the range of these expectations. We might even see a decade or more with little apparent change in sea ice. The causes of these fluctuations in melt rate are still being explored. One suggestion is that slow variations in Atlantic sea surface temperatures are involved. More observations of the Arctic ocean, atmosphere and sea ice would help answer this question. An ice-free future? When will the Arctic be ice-free – or equivalently, when will the ball reach the bottom of the hill? The IPCC concluded it was likely that the Arctic would be reliably ice-free in September by 2050, assuming high future greenhouse gas emissions (where “reliably ice-free” means five consecutive years with less than 1 million km2 of sea ice). We expect the long-term decline in Arctic sea ice to continue as global temperatures rise. There will also be further bounces, both up and down. Individual years will be ice-free sometime in the 2020s, 2030s or 2040s, depending on both future greenhouse gas emissions and these natural fluctuations. Even when it reaches the bottom of the hill the ball will continue to bounce. Similarly, not every future year will be ice-free in summer. But if global temperatures continue to increase the bounces will become smaller and the ice-free periods will spread from late summer into autumn and early summer. Commercial Arctic shipping is already increasing to exploit shorter journey times from Europe to Asia, while oil, gas & mineral extraction possibilities are being explored and Arctic tourism is growing. Decisions about such activities need to assess both the risks and opportunities. The important role of natural sea ice fluctuations needs to be considered in such assessments.

Picked up a quick 0.75 with a few CG strikes here in SW Suffolk.

Shorties that remain OTS aren’t what hurricane seasons are remembered for. The relevant metrics are landfall, intensity, rainfall, and seasonal ACE. But the higher number of named storm years usually feature a significant amount of major hurricanes.