Global Climate Change and its Potential Connection to Hurricane Activity (cited research)

Because of recent North Atlantic Hurricane Season activity…many people have questioned whether hurricanes are becoming stronger and more numerous because of climate change. In the social media universe, I’ve seen many opinionated debates within the general public, as well as meteorologists and perhaps a few sprinkling of climatologist opinions here and there. Not to mention, interesting statements from non-climate scientists. What I have not seen much, however, is any discussion of peer-reviewed research on the topic. There’s so much knowledge being gathered every year by scientists trying to answer important questions about our past, present and future. How climate change will impact regional weather and climates is one of the most important questions because of potential impacts to people, agriculture and natural resources.

I decided to do a (very brief) search of literature on science’s current understanding of climate change as it relates to tropical cyclones. I looked into both the potential connection of global warming to these events in the current climate (attribution), as well as projections for these events based on the “business-as-usual” scenario for carbon dioxide emissions, which is a high emissions scenario and steady increase in CO2 concentration. Research cited are just a sampling of what’s out there and what I looked over. Here are some themes I found interesting (takeaway statements at the end):

Climate models* appear to show a signal toward more intense (Category 4-5 Saffir-Simpson) tropical cyclones overall in the world by the latter half of the 21st century. However, there is also a potential for a downward trend in cyclone numbers in many basins (see #1-4).

The decrease in overall cyclone numbers by the second half of the century is thought to be a product of increasing vertical wind shear over tropical oceans limiting weaker storms. However, many researchers expect there to be a significant upward trend in more intense storms (Category 4-5) as the oceans continue to warm and tropical cyclone formation and track density moves poleward. So formerly less favorable sub-regions of basins may see an overall increase in cyclone activity (with more storms which will be stronger than before in those regions) and in the increasingly less hospitable regions (over the long term), storms which do form when conditions are favorable on short time scales may see cyclones which are also more intense than in years past.

As for historical conditions leading to the present…there does not appear to be a conclusive signature by global warming on tropical cyclone intensity outside of natural variability on a global scale (3-4). However, some regional signals related to frequency changes are being actively studied. 

There is some suggestion (4) based on modeling past climate change to the present time that warming (which would enhance the potential intensity for hurricanes) has been muted by the industrial production of aerosols (particulates like sulfates and nitrates), which actually reflect sunlight from reaching Earth’s surface. However, as warming continues into mid-century, its effect of trapping heat will begin to significantly exceed aerosol cooling effects leading to the more pronounced impacts on cyclone intensity stated earlier (unless CO2 emissions are significantly reduced soon). So while global warming is happening in the background, hurricane potential intensity as we currently witness it is likely still being dominated by natural cycles. (For more on climate change research into tropical cyclones, you can also see this webinar done by climate change researcher Dr. Kerry Emanuel for Climate Central).

With that said, some researchers see signs of a global warming signature associated with recent increased tropical cyclone *frequency* in sub-regions of basins. These include the far eastern portion of the North Atlantic Basin (4), close to the East Asian Coast (5), and a portion of the North-Central Pacific Basin (6). Research is still ongoing on global warming’s past and future influence on activity in individual tropical cyclone basins.

Meanwhile, there is evidence of other impacts related to tropical cyclones (and other significant weather phenomena) and climate change. These include higher rainfall rates (7) and higher storm surge related to sea-level rise from the melting polar ice sheets and thermal expansion of the oceans (8). In addition, there is some scientific evidence that tropical cyclones in recent decades have begun to intensify more rapidly because of increased ocean warming (9). And while not completely clear yet whether it is fully tied to climate change, it is known that the observed North Atlantic Power Dissipation Index (PDI) has increased significantly since the mid-1970s (10; positively correlated to sea surface temperatures) and globally, the strongest tropical cyclones in respective basins have grown stronger since 1981 (Elsner et al, 2008…not included here). Note that scientific critics point out the use of observational data with differences in quality – satellite intensity estimates and reconnaissance flights (or lack of them) – over recent decades could put some uncertainty in these results.

My thoughts? Although inconclusive, possible intensity signals may be a hint of the projected effects of climate change as PDI and high-end cyclone intensity are highly correlated to sea surface temperatures. SSTs are increasing from global warming and this would connect with what climate models suggest of future tropical cyclone activity, if these historical trends are, in fact partially related to climate change.

The Takeaways:

  1. Tropical cyclone intensity at the highest end of the scale appears likely to increase through the 21st century because of climate change, especially if human civilization does not significantly reduce greenhouse gas emissions soon.
  2. While a current climate change signal to intensity is difficult to detect and still a matter of debate, storms in recent decades appear to be intensifying faster, are capable of producing more extreme precipitation events and higher storm surges because of rising sea levels caused by ice sheet melting and thermal ocean expansion. There also appears to be some detectable changes in frequency of storms within individual basins which may locally enhance risk.
  3. Regardless of the exact changes in frequency and intensity of tropical cyclones, the risks to individuals and society because of climate change will increase into the coming decades. It will be important for people and governments to make decisions (beyond greenhouse gas emissions) related to property, coastal land use and emergency management policy to mitigate increasing tropical cyclone hazards, particularly from water (storm surge/inland flooding).

Note: It is of EXTREME importance that those with a desire to communicate climate change issues try to inform our fellow citizens to the best of our ability. Climate change is one of the important issues facing our world (the impact on the global food supply and human health may be actually of greatest importance, but rarely discussed as those aren’t “sexy” topics…). People have their thoughts on the issue based on experiences, politics, religious/spiritual beliefs, etc. However, at the end of the day, we must inform and connect what we know to people’s concerns and allow people to decide as they may. Without censorship (“We can’t discuss climate change right now!”) or nonsensical exaggerations (“So many hurricanes, it’s a new era of superstorms!”). Stay informed (give informed opinions) and tell people why they should care as it relates to their lives. Like everything else we should communicate to the concerns of people. Considering most Americans are now, in fact, concerned about climate change, there’s really NO excuse not to discuss the issue in a serious, informed manner if we have the interest to discuss it at all. 


Additional Note: *-Climate models are not weather forecast models. They do not forecast the atmosphere using initial conditions, but take a climate state (for example, our current climate) and adjust “forcings” on the climate system (carbon dioxide emissions for example). The effect of these changes to “boundary conditions” over time are interpreted for land, sea, the cryosphere and (for Earth System models), the biosphere. Global climate is based on thermodynamic and hydrologic balances which will look for equilibrium when changes to a part of the system are applied. (For more on climate models you can see this webinar by Research Meteorologist Keith Dixon of NOAA’s Geophysical Fluid Dynamics Laboratory for Climate Central).

References (links are PDFs):

#1 – Bell et al. (2013)

#2 – Murakami et al. (2011)

#3 – Wang and Wu. (2013)

#4 –  Sobel et al. (2016)

#5 – Cheng-lin et al. (2016)

#6 – Murakami et al. (2015)

#7 – Knutson et al. (2013)

#8 – Jevrejeva et al. (2016)

#9 – Kishtawal et al. (2012)

#10 – Emanual (2005)

—Meteorologist Nick Humphrey

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2016 State of the Climate: The Sobering Data

Today The American Meteorological Society, in collaboration with the National Oceanic and Atmospheric Administration released their yearly peer-reviewed “State of the Climate” report detailing the state of the global climate. It is…not positive at all.

You can see the full report HERE. But here are the bullet points:

-The report confirms, via independent datasets that 2016 was the warmest year on record for human observations (most world observations go back to mid-1800s). Not only for Earth’s atmosphere but for the Earth’s oceans.

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-The Earth’s surface averaged 1.06-1.21 degrees C above pre-industrial levels (depending on datasets available). It is the second year in a row the global land and ocean temperature averaged over 1 degree C. The “danger” zone for destructive impacts on human society and ecosystems around the world according to climate scientists is 2 degrees C or higher. Even 1.5 C would begin to have very hazardous impacts.

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-Global carbon dioxide concentration in Earth’s atmosphere (the main greenhouse gas being added by human activity) exceeded 400 part per million on average for the first time ever in human history. Not only that…This is the highest level in Earth’s atmosphere in at least 800,000 years based on data taken from ice cores. For comparison, pre-industrial levels of carbon dioxide concentration was approximately 280 ppm (only 150 yrs ago).

-The increase in the yearly average of carbon dioxide by 3.5 ppm from 2015 to 2016 is the largest increase observed in the 58 year history of observations.

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-2016 featured significant portions of land areas suffering from “extreme heat”…heat above the 90 percentile compared to the 1961-1990 average temperature for the location.

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-2016 was the warmest year on record for the ocean, causing major stresses for ocean ecosystems, including coral reefs. Over 90% of global warming heating goes into the oceans (100+ zetajoules (1 x 10^23 joules) since 1993…it takes ~4 joules of heat to warm 1 gram of water by 1 degree C…it takes A LOT of energy to raise the temperature of water).

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-Sea levels are rising nearly everywhere, at different rates. Added water and thermal expansion by the heating of water are both factors. This is the 6th consecutive year of increase.

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-Severe drought impacted at least 12% of the planet’s land area each month of 2016 for the first time in history. (Note: The drought conditions in the Amazon Rain Forest in 2015-16 the third “100-year” event since 2005 with previous events in 2005 and 2010).

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-Arctic sea ice had its lowest winter maximum on record and second lowest summer minimum on record in 2016. The mass of the Greenland Ice Sheet, which has ice up to 110,000 yrs old and has the ability to contribute to up to 7 meters sea-level rise is at a record low value.

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-2016 was the 37th consecutive year of worldwide Alpine glacial retreat.

-Across the Northern Hemisphere, snow cover was the 4th least extensive in the 47-yr record.

-Record high temperatures at 20 meters were observed at depth in permafrost observatories in Alaska and Canada.

-The United States had the 2nd warmest year on record in 2016 and the 20th consecutive warmer than normal year.


It’s interesting that this came out today because I was actually just beginning to write the draft to the next in the series of WxClimoEd “Understanding Global Climate Change“. But then this blew up my Twitter LOL. This pretty much gives me a good addition to what I would’ve discussed anyways. So let’s do just that…

It appears to me that we have crossed in the 2015-2017 period some crucial thresholds in the “era” of anthropogenic climate change. We are continuing to pump more carbon dioxide into the atmosphere than Earth can remove through natural processes. We are essentially heavily polluting our atmosphere with CO2. Earth itself appears to have become a “1 degree C” world in terms of average temperature and major impacts expected to develop as a result. In addition, while our atmosphere is heating up, our oceans are also taking in incredible amounts of energy, slowly heating up and it’s quite literally cooking our marine life, all while the oceans undergo acidification from the CO2 they are taking in which is also causing harm to ecosystems. Coral reefs are facing this head on along with hundreds of thousands of species with depend on them. This is discussed is in the documentary Chasing Coral, which I reviewed HERE.

This year…2017…continues to see further signs of major problems which were predicted to be likely results of climate change.

-The first six months of 2017 (January-June) was the second warmest on record behind 2016. It is also the second warmest on record for the United States.

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-July saw record heat for the Western US and Alaska including record July or all-time record maximum monthly temps and sea ice within range of the Arctic Ocean coast. Other cities such as Reno, NV and Salt Lake City had their hottest July’s ever. Miami set an all-time record hottest month ever. Death Valley, CA took its wild heat to another level with an average July temperature of 107.4 degrees F making it the hottest month ever recorded in the United States historical record.

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-Arctic sea ice is headed for (yet again) one of its lowest extents in the observational record.

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-Boreal forests continue to burn at an unprecedented rate not seen in the past 10,000 yrs. Most notably significant fires have broken out in Canada and in the peat of the Arctic on the border of the ice sheet on Greenland.

I’ll write more about the IMPACTS of climate change…estimates of global and regional effects that I intended on writing about hopefully later this week in my regular post series. But in short…we really have no time to lose on this. Governments and citizens MUST do what they can…from individual efforts to industry…to get carbon emissions down. The more carbon dioxide goes into the atmosphere and higher temperatures rise, the greater the uncertainty as far as resulting phenomena such as climate feedbacks which could either hinder or enhance climate change, the latter of course worsening the situation faster. We as humans, we live our lives and we really have no idea how fragile how our world really is. We must realize how destructive a force we are so we can be constructive to ourselves and our world instead.