The Earth Story

Movement of the Gulf Stream’s Destabilization Point

The Gulf Stream is the western boundary of the North Atlantic sub-tropical gyre that transports heat and salt from the Gulf of Mexico to the deep Atlantic. This mighty ocean current follows the coast of Florida up to Cape Hatteras in North Carolina after which it starts to meander like a winding river. This point is called its ‘destabilization point’ and it has been moving westward in the last 2 decades at the rate of 25 kilometers per year.

The Gulf Stream meanders have the potential to create underwater cyclones and troughs that stir the nearby currents. The recent migration of the destabilization point has enhanced the frequency of deep ocean stirring of the nearby Deep Western Boundary Current and these events have become more common since 2008.

The westward movement of the destabilization point is hypothesized to be related to the warming of shallow water along the continental shelf in the coastal region from Massachusetts to North Carolina (the ‘Mid-Atlantic Bight’). The interactions between the Gulf Stream and the Deep Western Boundary Current when they cross below each other at Cape Hatteras could be the reason for this new warming trend observed.

Image Credits: NASA http://bit.ly/2m2md3U

Source: http://bit.ly/2lgzjcl http://bit.ly/2m6llrQ

Why did the Sahel drought end?

The 1970s and the 1980s were a time of severe drought across the Sahel region, the semi-arid landscape just south of the Sahara desert. This drought was so severe it even defined pop culture in the 1980s, leading to the Band Aid and Live Aid music events. Although severe droughts have hit portions of this region since then, the continent-scale droughts of the previous decades finally broke during the 1990s.

The major droughts have several proposed causes, including changes in ocean temperatures around the Sahel and changes in wind patterns due to pollution. Some of these potential causes, such as the warming ocean surface waters, have only gotten more severe since the 1980s, so understanding exactly what caused the drought to break is key to understanding the future drought potential.

To try to answer this question, a team from the Max Planck Institute for Meteorology turned to climate models. Using these models, they could vary sea surface temperatures and wind patterns in specific areas of the globe to see what impact those changes had on rainfall patterns in the Sahel. The researchers found that warming in zones in the Atlantic and Pacific were plausible contributors to the drought during the 1980s, but the drought broke when warming in a different area took over.

The scientists ran simulations with no temperature change in the Mediterranean Sea and then the observed temperature change pattern and found that the drought only broke when they included the modern warming of surface waters in the Mediterranean Sea.

The warmer waters in the Mediterranean cause more evaporation and a little bit of that moisture makes it across the Sahara, where it feeds additional rainfall when it collides with other weather systems. This research therefore implicates warming of the Mediterranean Sea as the main cause of the end of that drought.

Using the models, the scientists could also put in future warming projections to see if the Sahel drought conditions were likely to return. Regardless of which ocean basin they tested warming in, the answer was the same – as long as warming continues in the Mediterranean Sea area, an additional supply of moisture is available to avoid the decade long drought and near desertification seen in the 1980s.

-JBB

Image credit: Oxfam https://flic.kr/p/ebQFB1

Original paper: http://go.nature.com/298p550

Coughing up Icebergs

The Jakobshavn outlet glacier is a marine terminating glacier (terminates into the ocean) that flows off the west-coast of Greenland. It is the largest outlet glacier in terms of drainage area in Greenland, as it drains ~6.5 percent of the Greenland Ice Sheet. During the last two decades the flow rate of this glacier has increased so much (summer speeds of up to ~46 meters per day) that it has attracted the attention of the scientific community.

The Jakobshavn is the fastest glacier in Greenland in recent times. So what are the processes that has felicitated such velocities? Well, glaciologists have modeled, observed, and identified three distinct stages of acceleration that has resulted in such high flow rates. Firstly, between 1990 and 1991, they noticed a retreat in the terminus (front position) of the Jakobshavn glacier by 2 to 4 kms. This retreat was followed by calving of thin ice (ice less than 400 meters in thickness) that was generated so that the glacier would reach an equilibrium state.

In 1998, the glacier experienced thinning at the terminus and inland (10 km from the 1990 terminus), and a retreat of the grounding line (the point along the glacier at which starts to float in the ocean). This increased the surface slopes which led to an acceleration in the flow rate. Again, the retreat of the grounding line resulted in several calving events between 1998 and 2002.

In the late summer of 2003, Jakobshavn lost its ice tongue (long sheet of ice projecting out from the coastline) to a major calving event that lead to a steep increase in flow velocities. This was followed by a reduction in the surface mass balance of the glacier due to surface melting and run-off (http://on.fb.me/1OcO3lH). Later in 2012, there was another large calving event that produced an iceberg the size of Manhattan (http://on.fb.me/1zHo0vV).

Icebergs produced from calving events at the terminus of the Jakobshavn Glacier slowly make their way down a long fjord into Davis Strait, where they melt and reduce in size before reaching the open waters of the Atlantic. Large icebergs (such as the one on the photo) need to reduce their size considerably before they float freely in the open waters. Historians believe that iceberg that sank the Titanic was calved from the Jakobshavn Glacier.

-Nate

Image Credits: Terminus of Jakobshavn – Nasa Ice, http://bit.ly/1XEhG18 Icebergs in the Davis Strait – James Balog, http://bit.ly/1P1qGvz

Source:

http://bit.ly/1RVTzYB http://bbc.in/1PN6DOO http://bit.ly/1nZi898 http://bit.ly/1RDwfOg

Additional Reading:

http://bit.ly/1RDwjh3

July 2015: Hottest month since temperature records began

In early August, we reported on the release of July temperature statistics from NASA’s Goddard Institute, one of several organizations that releases a monthly temperature summary (http://tmblr.co/Zyv2Js1sHu0vM). Since then, other groups have released their numbers, including NOAA, and their numbers include a very stark statement.

July 2015 was the warmest month since instrumental records began.

July is on average the warmest month during the year globally – it’s summer in the northern hemisphere and due to the arrangement of the continents and the currents in the ocean the middle of Summer for the Northern Hemisphere winds up being warmer than the Southern Hemisphere Summer.

We’re in the middle of the strongest El Niño event in almost 2 decades, and as a consequence we’re en route to the warmest year in the instrumental record. Putting all that together, July 2015 registered as the warmest year in recorded history, going back over a century.

July 2015 was 0.08°C warmer than the previous record holder for July. That may not sound like a whole lot, but it’s easily outside the margin of error of this measurement. The planet has warmed by about 1°C over the past century, and therefore that represents a jump equivalent to about a decade’s warming over the previous record holder, which occurred after the 1998 super El Niño.

Both the monthly and yearly marks being set in 2015 continue to be consistent with the rate of warming observed over the past century, with no obvious change in the planet’s response.

-JBB

Image credit: NOAA http://www.ncdc.noaa.gov/sotc/global/201507 http://www.ldeo.columbia.edu/res/div/ocp/pub/seager/Kang_Seager_subm.pdf http://www.cnn.com/2015/08/20/us/noaa-global-climate-analysis/

105 years Last week we noted that October 2014 was the 3rd consecutive month that was the hottest of that month ever recorded (see: http://tmblr.co/Zyv2Js1WHvY3B) Despite 2014 starting off with a few months that weren’t extremely hot, it seems likely that 2014 is going to be either the warmest year in recorded history or at least a close second. A remarkable testament to the extremely rapid climate changes of the last century is found at the opposite end of the spectrum. To find out what that means, click to read more.  Global temperatures have been accurately recorded at hundreds of weather stations around the earth for well over 100 years, allowing accurate comparisons across the last century+. So if this year is probably going to set a record for warmest of all time, when was the record for coldest year of all time set? Remarkably, based on actual measurements of temperature around the world…the world set its record for coldest year in recorded history in 1909.  It has been 105 years since 1909 and every single year since then has been warmer than that year. That is just a remarkable testament to how rapid and extreme the climate shifts have been since the industrial revolution began. Today, we regularly set the record for warmest year ever, but it’s been so long since the coldest year in recorded history that virtually no one on Earth remembers it. 105 years. If it weren’t for greenhouse gases, then the planet should occasionally set both the record for coldest and hottest years on record. That’s no longer the case. Here’s a useful video that pointed out how extreme the lack of “coldest years ever” truly is: http://tmblr.co/Zyv2Js1WQf6eu -JBB Image credit: NASA http://www.giss.nasa.gov/research/news/20110113/

Ocean surfaces hit record warmth in 2014 Increasing carbon dioxide in Earth’s atmosphere causes the planet to retain extra heat, but where that heat goes has proven to be complicated. Over the past decade we’ve begun to understand that there are many reservoirs that take up this extra heat. All of them have shown the effects of increasing warmth, but it has turned out that the patterns are quite surprising. The main reservoirs that can take extra heat, that we know about right now at least, include the atmosphere, the upper oceans, and the deep oceans, potentially as well as “melting ice” if it happens on a large enough scale. The ocean reservoirs are particularly huge. There is so much water in the oceans that even a small change in water temperature is an uptake of a huge amount of heat. Over the last 16 years, the atmospheric temperature has hit several record highs and it seems on course to do so again this year (http://tmblr.co/Zyv2Js1TsvMhq). Other recent work looking at sea levels has suggested that large amounts of heat have been stored in the deep oceans, enough to produce measureable changes in sea levels solely through thermal expansion (the property where almost all matter increases in volume as it gets hotter: http://bit.ly/1tl7Y6A).  However, for the last 10+ years, satellites and direct temperature measurements didn’t see much of a change in sea surface temperatures. This fact has led some to describe the situation as a “pause” or something like that in the long-term trend of increasing temperatures. As of 2014, that is no longer the case. The surface portions of the oceans saw a big temperature increase in 2014, blowing past the sea surface temperatures observed in the monster 1998 El Nino event. This change therefore makes the world’s oceans in 2014 as hot as they have been since before humans on sailing ships started dipping temperature probes into the waters. This 2014 heating was mostly concentrated in the North Pacific Ocean, which suggests that it could have a link to the extreme weather events throughout the world. The warm Pacific waters are in areas that likely contributed to the growing drought in California, as well as changes in Pacific Ocean typhoon paths and intensity and even coral bleaching near the Hawaiian Islands. It’s hard to directly link local effects to climate change as the weather on any given day is a complicated function of a whole lot of variables, not just the global climate, but this temperature record being driven by the Pacific Ocean does suggest a connection between 2014’s weird weather and a warming world. -JBB Image credit: NOAA http://www.eurekalert.org/multimedia/pub/82616.php?from=282303 Press release: http://www.eurekalert.org/pub_releases/2014-11/uoh-woe111314.php