Featured on National Geographic. "A lone freediver escapes to another world underwater where his impossible dreams become reality." "The Superman" is a labour of love project for directors Jack Pirie and Alex Hylands-White, made in collaboration with Freediver Francisco Del Rosario and Bamford Watch Department.
The short film follows Del Rosario, who lives on the remote island of El Hierro in the Canary Islands.
Thomas Karl and colleagues were harassed by Republicans for publishing inconvenient science. A new study proves them right.
A new study has shown that a 2015 NOAA paper finding that the Earth is warming more rapidly than previously thought was correct.
Once again, science is shown to work.
The laborious process in which
scientists check and recheck their work and subject their ideas to peer
review has led to another success.
An independent test of global warming
data has confirmed a groundbreaking 2015 study that showed warming was
faster than prior estimates.
Because of its inconvenient findings, the study’s lead author Thomas Karl was subjected to harassment by Lamar Smith (R-TX),
chair of the House Science Committee, in an effort to impugn his
credibility.
But now Karl and his co-authors have been vindicated.
Let’s
take a step back and discuss the science.
Measuring the temperature of
the Earth is hard.
There are many locations to measure and many choices
to make.
Should we measure the temperature of the ground? Of the ocean
waters? How deep in the water? If we measure air temperatures, what
height should the measurements be taken? How many locations should we
make measurements at? What happens if the instruments change over time
or if the location changes? What happens if a city grows near a
measurement location and the so-called urban heat-island effect grows?
How do we estimate the temperatures in areas where no measurements
exist?
Climate Change: Global Temperature Data
These and many other questions make measuring global warming
challenge.
Different groups of scientists make different decisions so
that depending on the institution, they will get a slightly different
temperature result.
But this diversity is also a good thing.
It turns out that it doesn’t
matter whose results you use – NASA, NOAA, The Hadley Centre in the UK,
the Japanese Meteorological Agency, or the Berkeley Earth group – they
all report a warming world.
However, the rates are slightly different.
So, one persistent question is, which group is most accurate? Whose
methods are best?
The new study looks into just this question.
The group focused on
perhaps the biggest differences among the groups – how they handle ocean
temperatures.
Specifically, global temperature values typically use a
combination of near-surface air temperatures in land regions and sea
surface temperatures in ocean regions.
Since oceans cover approximately
70% of our planet, the way ocean temperatures are dealt with can
separate the warming rates between these groups.
Ocean temperatures can be measured by ship-based temperature sensors,
by special floating measuring instruments, or by satellites.
Prior to
the advent of satellites and floating sensors, ships were the main
temperature sensing platforms.
Ship sensors, which measure engine intake
water, are known to be slightly warmer than the actual water.
So using
them introduces a warm bias in the measurements.
Annual Average Global Temperatures.
Both panels are calculated using a 1951-80 periodand represent the average Global Temperature index in degrees C.
At the poles where ice cover varies over the record we provide two cases.
For the baseline case the air temperature over iceis used for the average and in the alternative case in the bottom panel Sea Temperature under the ice cover is used. -1.8 C is used for this value in all cases
Also, as ships have gotten larger, the depth of the engine intakes
have increased – meaning the tested water was further from the actual
ocean surface.
Since the temperature results from buoys differs from
ship measurements, the various scientific groups have tended to try to
perform corrections between the different sensors.
The way the
correction is done affects the reported warming rate.
The authors recognized that one of the biggest questions is how to
stitch together different temperature results from different sensors.
Therefore, they broke the temperature data up into groups according to
the measurement device (buoys, satellites, ARGO floats, ships, etc.) and
they evaluated warming rates separately for each group.
The authors
also used advanced statistics to handle areas where no data were
recorded.
Berkeley Earth Global Temperature index, 1850 to present
After applying their tests, the authors found that the results
promoted by Karl at NOAA are the best, and other groups, in particular
the Hadley Centre in the UK and the Japanese agency, are too cold.
So what does this all mean? A few things.
First, this study is a nice
reminder that the proper way for science to work is for publications to
be scrutinized and checked by others.
This process leads the entire
scientific community to a deeper understanding of the science.
Second, this validates the scientists who were originally attacked by
political non-scientists and in some cases by contrarian scientists.
For instance, Judith Curry, a well-known critic of mainstream climate
science was quoted as saying:
The new NOAA dataset disagrees with a UK dataset, which is generally regarded as the gold standard for global sea surface temperature datasets … The new dataset also disagrees with ARGO buoys and satellite analyses ...
Color me unconvinced.
I actually study ocean temperatures so I knew this statement by
Judith Curry was complete nonsense.
It is nice to see a team actually
take the time to prove it.
Perhaps she and others will finally admit
they were wrong.
This paper is another reminder why it is so important to invest in
the temperature measurements that are needed to create long-term climate
records.
We really need uninterrupted measurements that span many
years/decades if we want to truly understand the Earth’s changing
climate.
Even though the costs of making these measurements are very
small compared to what we spend on other less important activities, I am
concerned that the new US administration will decide to pull the plug
on these projects.
If that happens, we will be flying blind.
Finally, and for those who read my posts regularly, I am sounding
like a broken record.
Global warming is happening, it never stopped, it
never paused, and the models have gotten it right.
It reminds me of a debate between creationists and scientists.
One
scientist whose name I cannot remember stated, “we have the fossil
record, we win.” Well, a similar quote works here.
“We have the data, we
win.” Now let’s move on to solving the problem.
The oceans are mostly composed of warm salty water near the surface over cold, less salty water in the ocean depths. These two regions don't mix except in certain special areas.
The ocean currents, the movement of the ocean in the surface layer, are driven primarily by the wind. In certain areas near the polar oceans, the colder surface water also gets saltier due to evaporation or sea ice formation.
In these regions, the surface water becomes dense enough to sink to the ocean depths.
This pumping of surface water into the deep ocean forces the deep water to move horizontally until it can find an area on the world where it can rise back to the surface and close the current loop.
This usually occurs in the equatorial ocean, mostly in the Pacific and Indian Oceans.
This very large, slow current is called the thermohaline circulation because it is caused by temperature and salinity (haline) variations. source : NASA
Intense future climate change could have a far different impact on
the world than current models predict, suggests a thought-provoking new study
just out in the journal Science Advances.
If atmospheric carbon dioxide
concentrations were to double in the future, it finds, a major ocean
current — one that helps regulate climate and weather patterns all over
the world — could collapse.
And that could paint a very different
picture of the future than what we’ve assumed so far.
The Atlantic meridional overturning circulation, or AMOC, is often described asa
large oceanic conveyor belt.
It’s a system of water currents that
transports warm water northward from the Atlantic toward the Arctic,
contributing to the mild climate conditions found in places like Western
Europe.
In the Northern Atlantic, the northward flowing surface water
eventually cools and sinks down toward the bottom of the ocean, and
another current brings that cooler water back down south again.
A slowdown or even collapse of the Gulf Stream System as a result of global warming has long been a concern of climate scientists and has fuelled the imagination of Hollywood.
Regular direct observations of this giant ocean current system do not go back far enough to tell whether there is any long-term trend.
However, in recent years indirect evidence is mounting for a remarkable slowdown over the 20th Century.
The
whole process is part of a much larger system of overturning currents
that circulates all over the world, from pole to pole.
But some
scientists have begun to worry that the AMOC isn’t accurately
represented in current climate models.
They say that many models portray
the current as being more stable than real-life observations suggest it
actually is.
Recent studies have suggested that the AMOC is weakening,
although there’s some scientific debate about how much of this has been caused by human activities and how much by natural variations.
Nevertheless,
the authors of the new study point out, many climate models assume a
fairly stable AMOC — and that could be affecting the predictions they
make for how the ocean will change under future climate change.
And
because overturning circulation patterns have such a significant effect
on climate and weather all over the world, this could have big
implications for all kinds of other climate-related projections as well.
“This is a very common and well-known issue in climate models,” said the new study’s lead author, Wei Liu,
a postdoctoral associate at Yale University, who conducted the work
while at the University of California at San Diego.
“I wanted to see, if
I use a corrected model, how this will affect the future climate
change.”
Liu and colleagues from the UC-San Diego and the University of
Wisconsin at Madison took a commonly used climate model and corrected
for what they considered to bethe AMOC stability bias.
Then they ran an experiment to see how the correction would affect the
model’s projections under future climate change.
They instantaneously
doubled the atmospheric carbon dioxide concentration from present-day
levels in both the corrected and uncorrected models, and then they let
both models run for hundreds of simulated years.
The differences
were striking.
This visualization composites Ocean Surface Flows over Sea Surface Temperature data from the Estimating the Circulation and Climate of the Ocean, Phase II project, depicting Earth's ocean circulation model that involves heat transfer.
In the uncorrected climate model, the AMOC weakens for a
while, but eventually recovers.
In the corrected model, however, the
AMOC continues to weaken and after 300 years, it collapses altogether.
In a commentary
also published today in RealClimate, Stefan Rahmstorf, an oceans
physics expert at the Potsdam Institute for Climate Impact Research,
explained how such a collapse could occur when the AMOC gets too weak.
“Freshwater
continually flows into the northern Atlantic through precipitation,
rivers and ice-melting,” he wrote.
“But supply of salty waters from the
south, through the Gulf Stream System, balances this.
If however the
current slows, there is less salt supply, and the surface ocean gets
less salty.”
Because freshwater is less dense than salty water,
this process can lead to a kind of stratification, in which the lighter
freshwater gets stuck on the surface of the ocean and can’t sink to the
bottom when it reaches the cooler north.
When this happens, the
overturning process that drives the current back down south again can’t
occur.
“There is a critical point when this becomes an
unstoppable vicious circle,” Rahmstorf wrote.
“This is one of the
classic tipping points in the climate system.”
The resulting
climate consequences, compared to the uncorrected model, are also
dramatic.
Without the usual transport of warm water into the north, the
corrected model predicts a marked cooling over the northern Atlantic,
including in the United Kingdom, Iceland and northwestern Europe, as
well as in the Arctic, where sea ice begins to expand.
Because the AMOC is part of a larger global conveyor system, which
ferries warm and cold currents between the equator and both poles, the
model predicts disruptions in other parts of the world as well.
Without
cold water moving back down south again, the corrected model indicates a
stronger warming pattern south of the equator than what’s predicted by
the uncorrected model, causing a polarization in precipitation patterns
over the Americas — more rain for places like northeastern Brazil and
less rain for Central America.
The model also predicts a greater
reduction in sea ice for the Antarctic.
This visualization shows Ocean Surface Current Analysis Real-time (OSCAR) ocean currents colored by current velocities.
OSCAR data (produced by Earth & Space Research and distributed through NOAA and PO.DAAC) is derived from observed satellite altimetry and wind vector data. OSCAR data is shown from January 1, 2008 through July 27, 2012.
Blues are slow currents, greens currents are about 0.5 meters per second, and red currents are about 1 meter per second.
All this doesn’t
necessarily mean that everything we thought we knew about the future
climate is wrong.
For one thing, most modern climate projections focus
on the next few decades or so, noted Thomas Haine,
an expert on ocean circulation at Johns Hopkins University.
And within
50 years or so, both the uncorrected and corrected models in the new
study produce similar results.
It is only after that, under extreme
warming, that the current shifts.
Liu also cautioned that certain
aspects of the experiment can’t exactly be considered realistic — for
instance, instantaneously doubling the atmospheric carbon dioxide
concentration.
Current climate efforts are aimed at keeping us from ever
getting to such a point — but even if we did, the process would happen
gradually, not overnight.
So the model’s outcome might have been
different if the researchers had adopted a more realistic scenario.
Haine
also suggested that the correction in the new study may have actually
been a bit too strong, compared to actual observations — in other words,
the modeled AMOC is “probably more unstable than the real system,” he
said.
Rahmstorf also pointed out this issue in his commentary —
but he added that the climate model used also did not account for an
influx of meltwater from Greenland under future climate change, an event
that recent research suggests could substantially speed the AMOC’s
weakening.
This visualization shows ocean current flows in the Mediterranean Sea and Eastern Atlantic from 16 Feb 2005 through 16 January 2006.
For each second that passes in the visualization, about 2.75 days pass in the simulation.
The colors of the flows represent their depths.
The white flows are near the surface while deeper flows are more blue.
“With unmitigated emissions . . .the Gulf Stream System weakens on
average by 37 percent by the year 2300 without Greenland melt,” he
notes.
“With Greenland meltwater this doubles to 74 percent.
And a few
months ago, a study with a high-resolution ocean model appeared,
suggesting that the meltwater from Greenland is likely to weaken the
AMOC considerably within a few decades.”
The fact that current
models don’t take this melting into account is further support for the
idea that scientists have been underestimating the risk of a future AMOC
collapse, he suggested.
According to Liu, the new study serves to make a point about the
dramatic effects that can occur when corrections are made in climate
models, as well as the AMOC’s major role in the global climate.
By
tweaking a climate model to make it more consistent with real-life
observations, very different outcomes may be observed, Liu noted.
“I
would say that it is reasonably well-accepted that a current generation
of climate models [is] missing the essential physics in representing
the AMOC,” said Haine.
And he added that the new study “points to the
need to fix these biases in the climate models.”
