Category Archives: Climate Change

We Migrate Five Days Later Now

Golden eagle at Allegheny Front Hawk Watch, 1 Nov 2016 (photo by Steve Gosser)
Golden eagle at Allegheny Front Hawk Watch, 1 Nov 2016 (photo by Steve Gosser)

Twenty-one years ago I attended my very first hawk watch on a spectacular golden eagle migration day — 26 October 1996 at the Allegheny Front Hawk Watch.

Nowadays when I want to see a lot of golden eagles I visit the Allegheny Front in early November because that’s when the eagles fly by.  Is it my imagination or are the birds migrating later than they used to?   A new study published last month in The Auk: Ornithological Advances confirms that raptors’ autumn migration has shifted later.

The study, conducted by Hawk Mountain Sanctuary, analyzed hawk count data for 16 raptor species from 1985 to 2012 at 7 hawk watch sites in eastern North America:  Hawk Mountain Sanctuary (Kempton, PA), Hawk Ridge (Duluth, MN), Holiday Beach (Ontario, Canada), Lighthouse Point (New Haven, CT), Montreal West Island (Québec, Canada), Mount Peter (Warwick, NY), and Waggoner’s Gap (Landisburg, PA).

The 16 species included both long distance migrants traveling to South America such as broad-winged hawks, and short distance migrants that stay in North America such as sharp-shinned hawks and golden eagles.  Each species adjusted its peak migration, but the delays were pronounced for short distance migrants.

To parse out the reason why raptors stay north longer, the study compared climate and air temperature data in the birds’ breeding areas to the timing of migration during the 28 year period.

As you can see from this NOAA map from October 2012, the climate warmed in the breeding zone in eastern North America (marked with a yellow square).  Click here to see the details on the study’s map.

Land & Ocean Temperature Anomalies, 1981-2010, NOAA (image from NOAA) Yellow square shows region of the hawk migration study.
Land & Ocean Temperature Anomalies, 1981-2010, NOAA (image from NOAA) Yellow square shows region of the hawk migration study.

Because the warming climate delays the first frost, plants and insects remain abundant later in the year. This abundance ripples all the way up the food chain to raptors who postpone their fall departure.  The study found that the shift in migration matches the pace of warming climate.

Golden eagles demonstrate the trend. Between 1985 and 2012 they waited an additional 0.16 days/year before moving south.  By 2012, the delay was 4.48 days.   Extrapolating to 2017, golden eagles are leaving 5.12 days later now than they did in 1985.

Whats’ more than five days after October 26?   November 1.  So I’m going to the Allegheny Front Hawk Watch in November.

Click here to read about the study and download the full report.


p.s. Three species have delayed autumn migration even more than golden eagles: Sharp-shinned hawks added 0.2 days/year, northern goshawks added 0.21 days/year and black vultures added 0.40/year.

(photo by Steve Gosser)

Sea Level Fingerprints

Fingerprint image from Wikimedia Commons
Fingerprint image from Wikimedia Commons

As ice sheets melt around the world, fresh water that used to be held on land is pouring into the ocean and sea level is rising.  But it’s not rising uniformly.  The transfer of mass (water) from land to sea causes changes in Earth’s gravity field.  Mirroring the ripples in gravity, the water is high in some places and low in others like the ridges on a fingerprint.

The mysteries of gravity *

Gravity is a force of attraction.  It works on everything and in both directions. The Earth’s mass pulls you toward it while your mass pulls Earth toward you.  The bigger the mass, the stronger the object’s gravitational pull.  Greenland with an ice sheet on top has more mass than Greenland without one, so as the ice melts Greenland’s gravitational pull goes down.

As Greenland’s gravity wanes it doesn’t hug the ocean to its shore like it used to.  The water has to go somewhere so it rises in the tropics.  The effect is tiny, measured in millimeters per year.   The pattern is called a sea level fingerprint.

The pattern revealed

Many things contribute to sea level at any given point including the Moon’s gravitational pull (causing tides) and the wind (causing waves) so it took lots of data and some serious number crunching to reveal Earth’s gravitational fingerprint.  The data came from the GRACE satellite project.

GRACE satellites have been circling the Earth since 2002, measuring the pull of gravity on the globe below.  (Here’s how GRACE works.)  Each orbit provides a snapshot.  Years of data show the change in gravity over time.  Most gravitational changes are due to the movement of water, especially groundwater.

Using GRACE data, scientists from NASA and the University of California Irvine mapped gravitational changes affecting sea level from 2002 to 2014, shown on the map below.  Blue means low water, red is high. The calculations were verified using readings of ocean-bottom pressure from stations in the tropics.

Sea level fingerprints (patterns of variation in sea level rise) calculated from GRACE satellite observations, 2002-2014. The blue contour (1.8 millimeters per year) shows the average sea level rise if all the water added to the ocean were spread uniformly around Earth. Image credit: NASA/UCI
Sea level fingerprints (patterns of variation in sea level rise) calculated from GRACE satellite observations, 2002-2014. The blue contour (1.8 millimeters per year) shows the average sea level rise if all the water added to the ocean were spread uniformly around Earth.
Image credit: NASA/UCI

Notice that the ocean has receded the most near Greenland at the rate of -2.5 mm/year.  That’s 32.5 mm or 1.28 inches in the 13 years that GRACE measured it.  As NASA explains:

The loss of mass from land ice and from changes in land water storage increased global average sea level by about 0.07 inch (1.8 millimeters) per year, with 43 percent of the increased water mass coming from Greenland, 16 percent from Antarctica and 30 percent from mountain glaciers.

Click here to read more about the study and see an animated map of sea level changes 2002-2014.

Unfortunately some of the hardest hit places will be tiny Pacific islands and Florida.

Who knew that the sea has a “fingerprint.”


(fingerprint image from Wikimedia Commons; click on the caption link to see the original. Sea level fingerprint map from NASA/UCI joint project using GRACE satellite data)

* p.s. Gravity is so mysterious that I initially described it incorrectly.  Thanks to Dr. Allen Janis, I’ve corrected the description. See his comment below.

Warming Up to the Next Ice Age

screenshot from This Is Not Cool with Peter Sinclair, Yale Climate Connections
screenshot from This Is Not Cool with Peter Sinclair, Yale Climate Connections

The ocean is warming, the ice sheets are melting, and the sea is rising. Does global warming mean we’ll be warmer here in the northern hemisphere?  Maybe not.

In this video by Yale Climate Connections, Jørgen Peder Steffensen, an expert in ice core analysis from the Niels Bohr Institute, explains how the Earth can become hotter yet simultaneously plunge Europe into an ice age and North America into ice or drought.  It’s a matter of distribution.

Here are some points that stunned me in the video:

  • In the last 1 million years there have been 10 ice ages.  Each ice age lasted about 90,000 years.
  • Ice ages aren’t uniformly cold. Far from it!  Steffensen says, “Inside an ice age the climate is extremely unstable, and you have this sequence of abrupt climate changes [semi-cold to very cold] that happen basically from one year to the next.”
  • In-between ice ages are interglacial periods of milder, more stable climate that last about 10,000 years. We’re in an interglacial period right now.  It’s already 11,000 years old.
  • Earth can have an ice age in one place and be hot elsewhere.  Ice cores indicate that when Greenland has an ice age, Antarctica is warm — and vice versa.
  • Earth’s current mild climate is due to a global distribution pattern of ocean currents and pressure systems that keep temperatures mild and rainfall moderate.
  • The global distribution pattern can change abruptly.  We don’t know where the trigger is, though we do know our emissions add fuel to the fire.

As Steffensen says, “The climate does not play nice all the time,”

Learn more at Yale Climate Connections:  Humans experimenting with climate’s ‘playing nice’


(screenshot and video from This Is Not Cool with Peter Sinclair, Yale Climate Connections)


Fewer Mild Weather Days

Mild weather during the Cherry Blossom Festival in D.C., 2006 (photo by Andrew Bossi via Wikimedia Commons)
Mild weather during the Cherry Blossom Festival in Washington, D.C., 2006 (photo by Andrew Bossi via Wikimedia Commons)

Ah, the mild days of spring!  You know the days I’m talking about, the ones that are perfect for birding, gardening, picnics and outdoor weddings.  The not-too-hot, not-too-cold, not-too-wet weather that makes you happy to be outdoors.

Unfortunately Pittsburgh will have fewer of them in the future. That’s what scientists from NOAA and Princeton University found out when they studied how the warming climate will affect our pleasant weather.

The loss has begun already though you may not have noticed it. For the last 35 years (1980-2015) earth’s climate has been converting 1 nice day per year into something unpleasant, mostly in Brazil, Africa and the Middle East.

By the end of the century the change will affect us.  The world will lose 10 mild days out of 74 but the loss won’t be evenly distributed.  The tropics will lose even more mild days while Canada, Maine and the Rockies can look forward to a pleasant future.

Here’s what our future looks like on the map.  Notice how the eastern U.S. is light orange indicating a net loss.

Change in Number of Mild Weather Days by 2090 (map from Van der Wiel/ NOAA/ Princeton)
Map showing the change in the annual number of mild days across the globe comparing 1986-2005 to 2081-2100. Areas of blue have increased in mild days. Areas of brown see a decline. (Van der Wiel/ NOAA/ Princeton)

That map shows the annual change but in fact it will vary by season.  For instance, Pittsburgh will gain some mild days in the fall (maybe 15) but lose more than that in the summer (25 to 50).  June-to-August will be hot!

Changes in the number of mild weather days by season by 2090 (map from Van der Wiel/ NOAA/ Princeton)
Changes in the number of mild weather days by season for 2090 (maps from Van der Wiel/ NOAA/ Princeton)

The full report includes details on mild weather in major cities at: Shifting patterns of mild weather in response to projected radiative forcing.

Now, more than ever, mild weather is a gift.  Enjoy it while you can.


(photo by Andrew Bossi via Wikimedia Commons; click on the image to see the original.
Climate map screenshots from Shifting patterns of mild weather in response to projected radiative forcing

(*) “Mild weather” is defined as temperatures between 64 and 86 °F, only a trace of rain (less than 0.04 inches) and low humidity (a dewpoint below 68 °F).

I’m Moving Northward

Carolina chickadee in North carolina (photo from Wikimedia Commons)
Carolina chickadee in North Carolina (photo from Wikimedia Commons)

Last week I wrote about Pittsburgh’s Puzzling Chickadees and promised to tell you why we have fewer black-capped chickadees every year.  The reason is: Our winters are getting warmer.

The Pittsburgh area is squarely in the contact zone where black-capped (Poecile atricapillus) and Carolina chickadees (Poecile carolinensis) meet and hybridize.  Black-capped chickadees can survive cold winters so they live north of the zone.  Carolinas cannot; they live in the south.

The contact zone snakes from New Jersey to Kansas, dipping south along the chilly Appalachian Mountains.  Studies by Robert Curry and his team at Villanova University found that the contact zone is located where winter low temperatures average at or above 14 to 20oF.

In 2010 David Sibley drew the contact zone for his Distinguishing Black-capped and Carolina Chickadees article. Click on the screenshot to see his original map and zoom it for your area.  The map is about 7 years old.

Screenshot of David Sibley's map of the black-capped and Carolina chickadee contact zone in 2010 (click on the map to see the original and zoom it in for your area)
Screenshot of David Sibley’s map of black-capped and Carolina chickadee contact zone approximately 2010. Click on the map to see Sibley’s original article and zoom the map for your area.


Seven years make a difference.  During that time the zone moved north almost 5 miles.  Here’s why:

Chickadees don’t migrate but young birds disperse to find a breeding territory.  The easiest territory to claim is an “empty” place where there aren’t competing birds of the same species.  For Carolina chickadees, that place is on the northern edge of the contact zone.

In 2000-2002 and 2010-2012, Robert Curry and his team measured winter temperatures and conducted DNA tests to identify chickadees in study plots north, south and inside eastern Pennsylvania’s contact zone.

The studies showed that over the 10-year period winter average low temperatures moved north 0.7 miles per year. They also found that female Carolina chickadees are dispersing further than their usual 0.6 miles.  They’re moving 0.7 miles northward in lock-step with climate change.

What does this mean for you?

If you live on the northern edge of the contact zone your chickadees can change in a year or two from 100% black-capped chickadees to a mix including Carolinas and hybrids.  On the southern edge it’s just as interesting as the black-cappeds disappear.

So don’t take Pittsburgh’s chickadees for granted.  The contact zone is moving northward.


(photo from Wikimedia Commons, map screenshot from David Sibley’s blog: Distinguishing Black-capped and Carolina Chickadees.  Click on each image to see the original.)

A Bad Month For Maple Syrup

Maple trees with sugar pails (photo from Wikimedia Commons)
Maple trees with sugar pails (photo from Wikimedia Commons)

There’s snow in this picture but there hasn’t been snow in Pennsylvania’s Laurel Highlands for half of this month.

March is supposed to be the best month for tapping sugar maples to collect sap for maple syrup.  The sap runs best with daytime temperatures above freezing and nights below freezing.  When the nights don’t freeze the sap stops running and the season is over.

This year Somerset County’s maple season was hampered by bursts of extremely warm weather in January and summer-like temperatures this month.  The thermometer hasn’t dipped below freezing since February 17 and some days have been more than 20oF above normal.  Maple sugaring stopped before it should have reached its best.

This trend isn’t unique to southwestern Pennsylvania.  The maple syrup industry tracks what’s happening to maple farmers from Virginia to Maine. Since 1970 they’ve noticed that the seasons have become shorter and the sap is less sweet so it takes more sap to make the same amount of syrup.

No matter where you stand on climate change the people whose livelihoods depend on cold winters (maple sugar farmers and ski operators) can tell you this:  Whacky climate ruins their business.

Read more here in a 2014 article from the Allegheny Front.


(*) Today the weather is yo-yoing again.  Meyersdale, PA will dip below freezing tonight (25 Feb) for two nights, then run up again to a 48oF low on Tuesday 28 Feb.

(photo from Wikimedia Commons. Click on the image to see the original.)

UPDATE on 7 March 2017: Here’s more on this year’s maple sugar season from the Allegheny Front, WESA-FM.

Red-tailed Hawks Adjust Their Plans

Red-tailed hawk (photo by Cris Hamilton)
Red-tailed hawk, 2012 (photo by Cris Hamilton)

If you don’t look at all the data you’ll probably be fooled.

For the past 30 years the number of red-tailed hawks migrating past hawk watches has declined across North America except at certain western sites.  With only this information to go on, you’d think that the species is in trouble.

But Neil Paprocki of HawkWatch International and his colleagues looked further. They compared hawk watch counts to the data gathered during Christmas Bird Counts in December-January and found that since 1984 red-tailed hawks have stayed in northern latitudes in much greater numbers.  They noted that red-tail counts declined at 43% of the hawk watches and increased on 67% of the Christmas Bird Counts.

As the climate warms and the winters are milder there’s less snow cover in the northern latitudes so it’s easier for the hawks to find food.  Fewer of them are bothering to travel south.

Red-tailed hawks are adjusting their plans.


Read more about the study here in The Condor: Combining migration and wintering counts to enhance understanding of population change in a generalist raptor species, the North American Red-tailed Hawk.  Laurie Goodrich of Hawk Mountain Sanctuary was a member of the study team.

(photo by Cris Hamilton)

Variably Icy

Icy path in Schenley Park, Feb 2015 (photo by Kate St. John)
Icy trail in Schenley Park, Feb 2015 (photo by Kate St. John)

Snow, sleet, rain, freezing rain.

From 5 degrees F on Thursday night to 53 degrees with freezing rain today, we’ve had it all.  And there’s more to come.  Tomorrow night will be 15 degrees.

This yo-yo weather reminds me of what we learned during the polar vortex in January 2014:  Climate change is making the jet stream wobble so we get shots of very cold air and then warm air soon after, as shown in drawing(c) below.

Jet stream Rossby waves (graphic from Wikimedia Commons)
Jet stream Rossby waves (graphic from Wikimedia Commons)


Be careful today!  It’s variably icy out there.


p.s. I’ve used an old photo of ice because it’s too icy to step outside this morning!

(photo by Kate St. John.  Drawing from Wikimedia Commons; click on the image to see the original)

More Robins, Fewer White-throated Sparrows

American robin, white-throated sparrow (photos by Marcy Cunkelman)
American robin, white-throated sparrow (photos by Marcy Cunkelman)

We humans are starting to respond to climate change. The birds already have.

In a study on two continents — North America and Europe — data from 1980 to 2010 shows that populations of our common birds have been affected by climate change and the gap is growing.  Bird species expected to do well due to climate change have substantially outperformed those expected to do badly over the 30 year period.  It’s the first real demonstration that climate is having a similar, large-scale influence on the abundance of common birds in widely separated parts of the world.(*)

Here are two examples from North America:

American robins are an adaptable species whose range has expanded as the climate warms.  Robins don’t have to go as far south in the winter and now they breed in Alaska!

White-throated sparrows are a common winter species in the Lower 48 but when it comes time to breed they’ll be in trouble.  As they move north the forest they require for breeding gives way to treeless landscapes.  It takes decades to grow a forest and climate is changing faster than the plants can catch up.  White-throated sparrows are losing ground.  Click here to see their changing map.

More robins, fewer white-throated sparrows.  The populations of common birds are affected by climate change.

Read more about the study here in Science Daily(*).  See Audubon’s climate website for details on North American birds.


(photos by Marcy Cunkelman)