I had considered writing an accounting of all the outlandish weather events of 2015, but that project quickly became a tl:dr list of untoward happenings which is both alarming and a bit boring, since it is so long. So, I decided to generate something less comprehensive, focusing more on the context and meaning of the diverse and impressive set of outcomes of anthropogenic global warming, an historically strong El Niño, and, well, weather which is already a pretty whacky thing.

See: Highlights of Climate Change Research in 2015

It should be noted right away that 2015 is the last year in which any human alive will see CO2 levels dip below 400 parts per million.

What is the biggest single weather related news of 2015?

Floods, probably. Around the world, there were a lot of floods, and a lot of them were very damaging and deadly. Also, many of these floods appeared with little warning, even in places like Texas, where the meteorology is pretty good. Those Texas floods were of special note, as were the floods in the Carolinas. But outside the US there were major floods in Asia, especially Vietnam and Myanmar, as well as Yemen. Alaska, Oklahoma, Atacama in South America, also saw severe floods.

Why were there so many floods?

I’m pretty sure it is accurate to say that there was more flooding, and more severe flooding, than typical for, say, 20th century climatology. We had many 1,000 year flood events, too many to assume that these events remain as 1,000 year events.

See: Global Warming Changing Weather in the US Northeast

There are probably two or three reasons for increased flooding, which of course is caused by increased and concentrated rainfall along with other factors such as land use changes that cause rainfall to result in more flooding. One is the simple fact that a warmer atmosphere, due to global warming, contains more water, and thus, we get more rain. How much more? Not a lot, but enough to make a difference. If you put together a bunch of weather data and plot the annual precipitation rate over the last century or so, and fit a line to the data, the line will look flat. It isn’t really flat, and in fact, a properly fitted line on good data will show a statistically significant upslope. But still, the total amount of extra precipitation is a small percentage of the usual amount of precipitation, so the slope is not impressive unless you draw it out using heavy-handed graphing methods.

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A few other places are doing end of year reviews. Inside Climate is doing a series of 2015 retrospectives. Skeptical Science has an overview of the year. Environmental health news has a wish list pivoting on 2015 and a year in review. And Then There's Physics summarizes 2015. Critical Angle takes a critical look at 2015 here. If you see any more out there in the wild, let me know. Media Matters has "The 15 Most Ridiculous Things Conservative Media Said About Climate Change In 2015." Media Matters also has 5 New Year's Resolutions For Reporting On Climate Change. HotWhopper has The Fake Sceptic Awards for 2015 here.
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A second factor is a set of changes in how, when, and where the rain falls. Normally, in the temperate regions, rain storms move along with trade winds, guided or influenced by jet streams, fairly quickly. But if the jet streams slow down, the storms slow down, so we may see 4 inches of rain fall in one place that normally would have been spread out over a larger area, never exceeding half (or less) of that amount in any given area. The jet streams have slowed down and also become curvier, which both increases the amount of rain that falls in a give area but also may transfer moisture from and to places that are normally not involved as much in such a process. For example, the storm we are expecting today in the upper Midwest and Plains is not a typical Canadian Clipper, but rather a Gulf Coast storm related to the deadly blizzards and tornado swarms we’ve seen over the last few days to the south.

See: Does global warming destroy your house in a flood?

This clumping of rain in smaller areas also means that other areas that would normally have received some rain don’t, causing what my colleague Paul Douglas refers to as “flash droughts.” These are dry periods that don’t last long enough, and are not severe enough, to register on any official drought-o-meter, but nonetheless stress local water systems (such as farming) enough to be a nuisance.

A third factor is sea surface temperature. This really relates to, and is probably one of the main causes, of the first factor (increased precip overall), and feeds into the second factor (clumping of rain) but deserves its own consideration. Elevated sea surface temperatures in the Atlantic off the US coast last winter caused a lot more moisture than normal to feed into nor’easter storms, which in turn have become more common (because of increased sea surface temperatures and other factors), thus dumping large quantities of snow in the US Northeast. The same thing dumped lots of extra snow in a region that normally gets very little snow, the US Southeast, the winter before.

See: A selection of books on climate change

These changes have been happening for decades, and are due to global warming. The warming caused by the human release of extra greenhouse gasses, and other human effects, increase the warmth, thus the evaporation, thus the precipitation. Part of this warming trend involved increasing the warmth of the Arctic at a much higher rate than most of the rest of the planet. This, in turn, seems to have caused the jet stream to become wavy and slow down. The jet streams and trade winds are ultimately caused and controlled by the Earth spinning, which has not changed, and the temperature differential between the warm equator and the cold poles, which has changed quite a bit.

See: Weather Whiplash Is Like My Old Broken Sprinkler

But what about El Niño?

Didn’t El Niño cause these changes, and thus, aren’t these weather events unrelated to global warming?

No, and for two reasons.

First, many of these events happened during the first half of the year, before the start of the current El Niño, which is in fact the strongest El Niño so far observed directly, and possibly the strongest El Niño in millennia.

The second reason is that the heat released by the El Niño (the release of heat stored in the Pacific Ocean is what an El Niño is, in functional terms) is added to an already warmed world. It may even be that the extra severity of this year’s El Niño is upscaled by anthropogenic global warming. In any event, any records we set during the current El Niño exceed earlier El Niño years because the El Niños we experience are shorter term warming events on top of a steadily increasing global warming phenomenon.

We had a lot of fires

Last year and this year, or really, the last few years, have seen excessive, above normal rates of forest and brush fires in various regions. We have seen major fires in Australia, North America, and Southeast Asia during this period, with North America breaking several recent records this year.

See: Forest fires in Indonesia choke much of south-east Asia

These fires are caused by a combination of factors, but ultimately heat increasing evaporation, prior rainy years increasing available fuel, and warm winters increasing tree death to parasites (thus increasing fuel), all have contributed.

North America, in the old days, had much more fire-heavy years than anything recent because we were busy cutting down the forest, piling up “slash” (left over tree parts) and running sparky old fashioned coal-driven railroad engines up and down between the slash piles, catching them on fire. In addition, just burning the slash on purpose contributed to the overall amount of fire, especially when the slash fires got out of control.

We also saw some pretty impressive fires a couple of decades ago because of what we now know were bad fire management practices, which had actually grown out of those earlier decades of logging related fires. In other words, the frequency and distribution of forest and brush fires is complex. During aridification, probably global warming related, in Africa during the 70s and 80s, vast areas started to burn more regularly than usual. In those days, I would fly at night over Libya, Chad and the Sudan a couple of times a year, and could observe the entire region was burning all the time, easily visible from 26,000 feet.

The bottom line: The frequency and extent of fires is variable and chaotic, but anthropogenic global warming seems to have contributed significantly to us having more of them.

Were there more storms in 2015?

Record breaking tropical storms occurred in 2015. All of the tropical cyclone/hurricane basins saw interesting activity, with the Atlantic being the most quiet, and the Eastern Pacific, possibly, being the strangest.

There were 22 Category 4 or 5 storms this year in the Northern Hemisphere, a record number. The last record year was recent, 2004. Studies have shown overall that the total energy that forms up in tropical cyclones has increased with global warming, though the actual total number of storms is highly variable.

It is reasonable to expect an increase in the frequency and severity of tropical storms with global warming, while at the same time, in some areas, smaller storms may become less common. This is partly because smaller storms are more readily abated by some of the global-warming related changes in weather systems such as increased wind shear and increased dust in the tropical atmosphere. At the same time, extremely high sea surface temperatures, and also, high water temperatures as depth (100–200 meters) increase the potential strength of storms that do get past that initial formation.

Hurricane Patricia, in the Eastern Pacific (landfall in Mexico) was an especially important storm. It was a physically small storm, but had more powerful winds than ever seen in a tropical storm. The storm went from nothing to a full hurricane in several hours (instead of several days).

The significance of this can not be underestimated. We have a situation where the conditions that might cause a hurricane to form are extreme, because of global warming (and this year, more so because of El Niño). So, when when these conditions are in place, a hurricane can form faster, and get more powerful, than normal. Consider the prospect of a land falling Category 5+ storm forming offshore from an area with low lying terrain (not like where Patricia struck land) with a high population density (not like where Patricia struck land) and moving on shore immediately. Like for instance, an Atlantic or Gulf of Mexico version of Patricia making landfall near Miami or NOLA.

Most of the really large hurricanes of this year were in the Pacific basin, distributed across the entire region, but Hurricane Joaquin, which was a very large and powerful storm in the Atlantic, did have us on the edge of our seats for a while when some of the better weather predicting models suggested it might make landfall. Also, nearly unprecedented tropical storms formed near the Arabian Pennensula.

This was a hot year

Other than February, which was merely hot rather than really hot, globally, every month so far this year has broken or nearly broken one or more records, depending on which database one uses. The running 12-month average of surface temperatures started to break records before El Niño kicked in, and continued to do so since. This will continue for several more months, even if the El Niño phenomenon itself stops soon, because it takes several months for surface temperatures to show the El Niño effect.

More specifically, there were killer heat waves in the Western Cape of South Africa, South Asia, and the Middle East. Australia recorded its hottest day ever. North America experienced numerous record breaking days, in the US and Canada. Cherry trees thought it was spring and bloomed last week in Washington. I saw birds building a nest outside my house in Minnesota two weeks ago, and our lawn was green(ish) through last weekend.

Ocean Oddness and Other Events

Let us not forget the Great Blob of Hot Water in the northern Pacific. This non El Niño phenomenon, which has been going for a couple of years no, has had El Niño like effects in the region, and probably relates to the non normal weather in along the western coast of North America, including record breaking heat in Alaska, major storms in or near Alaska, and of course, the California Drought.

A Haboob-Nado in China involved some of the strongest winds ever seen in the region, and may have, very unusually, contained an embedded tornado. We had a mild tornado season in the US, in Tornado Alley, until a few days ago when a not-very-seasonal tornado season sprung up and killed close to 50 people in just a few days. The American southeast does get winter tornadoes, but Michigan does not. But this year, there was a first ever recorded December tornado in that state.

The Arctic Sea ice has been diminishing in its minimum extent for a few decades now, and this year we saw the third lowest amount. The volume of Arctic sea ice continues to shrink.

You all know about the Syrian Refugee crisis. This is the latest chapter in the collapse of the Syrian state, which in turn happened because of long term drought in that country killing off the agricultural system and forcing farmers into the cities, where many became involved in the Syrian Civil War, which opened up the opportunity for the Islamic State to take a large amount of territory in the region. And so on. The Syrian refugee crisis is likely to be an early version of more of the same to come over future decades. And, I quickly point out, this is not likely to have been the first climate refugee situation, just much worse than prior events related to the spread of deserts in North Africa and drying out in West Asia.

Research on Climate Change

This year saw some interesting research in climate change.

One team studies major oscillations in climate that relate to oceans (of which El Niño is a shorter-term smaller part). This research suggests that the last couple of decades have seen less warming than we might expect over the long term, and further suggests that an uptick in the rate of warming is in our medium term future.

Related research also shows that accelerated melting of northern glaciers, especially Greenland, could alter Atlantic currents, so while the Earth generally warms due to increased greenhouse gasses, weather may change to a colder regime in Europe, some time over the next few dedades.

We are seeing an increased rate at which climate and weather experts are attributing bad weather to global warming. This is partly a shift in thinking and methods among the experts, and partly because of an actual increase in such events.

There has been interesting research in the Antarctic. We are seeing increased concern about, and evidence for, destabilization of huge inland glaciers that could start to fall apart and contribute to sea level rise at any time in the next several years. At the same time we saw one study that seemed to suggest that Antarctic is gaining ice, rather than losing it. If that is true, than recent decades of sea level rise are partly unexplained. Alternatively, the research, which has some known flaws, may simply be wrong. Look for some interesting results related to Antarctic glacier during 2016.

The famous #FauxPause in global warming, claimed by many climate change deniers to be a real thing (no warming in X years, etc.) was already known to be Faux, but this year saw several independent nails being driven into that coffin. Rather than a pause that disproves global warming, we have a better understood series of changed in the long term warming in the planet’s surface temperature.

See: In a blind test, economists reject the notion of a global warming pause

Sea floor biotic diversity was shown to be threatened by warming, coral bleaching is more likely and in fact happening at a higher rate, and probably mostly due to El Niño, there has been some odd ocean animal migrations.

The planting zones, the gardening and agricultural zones we use to decide which crops to plant and when, have over the last several years shifted in most places in North America by one or two zones. This year, the people who make the zone maps came out with a new one.

Sea levels continue to rise, and the rate of rise is rising. Rare nuisance flooding in coastal areas, most famously but not only Miami, have become regular events. Sales in waterproof shoes are expected to increase.

Communication and Politics

Across meteorology we see the graph and chart makers scrambling to find new colors for their maps showing heat. Y-axes are being stretched everywhere. We seem to be stuck with a five level category system for tropical cyclones/hurricanes, but we are seeing so many storms that are way stronger, bigger, more destructive than earlier Category 5 storms that talk of adding a category is no longer being responded to with angry mobs of pitchfork wielding weather forecasters who came of age with the older system.

See: How to not look like an idiot

There has been a great deal of significant climate change related activism, and COP happened, with a strong message to address the human causes of climate change sooner than later. Climate change has actually become an issue in US elections. For the first time a major world leader, President Obama, has faced off with the deniers and told them to STFU. Major news outlets such as the Washington Post and the Guardian have started to take climate change seriously. The idea that reporters must give equal weight to the “two sides of the story” (science is real, vs. science is not real) is disappearing.

Denial of climate change and climate change science reached its high water mark over the last 12 months. It will now fade away.

And that is a short and incomplete summary of weather and climate in 2015.

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A note for my regular readers: Yes, I chose the burning Earth graphic to annoy the denialist. Check the comments below to see if that annoyed anyone.