Posted: September 19th, 2022

The article you find must be related to the course information this week. At least 600 words You are expected to submit a summary of a current climate / environmental-related article from the mainstream press, along with your personal evaluation / refle

Geograph110_20_globaltemperatureIV3 Geograph110_22_thequestionofattribution4

The article you find must be related to the course information this week.

At least 600 words

  1. You are expected to submit a summary of a current climate / environmental-related article from the mainstream press, along with your personal evaluation / reflection. Using a recent news article from a reliable source, please feel encouraged to explore topics that include extreme weather (e.g. winter storms, drought), climate change, energy (e.g. decreases in crude oil price, fracking, coal mining, nuclear power plants, alternative energy, etc), adaptation of animal behavior to recent climate change (including mammals, insects, fish, etc), policy related topics (international climate change conferences), and more. Due by April 16th.
    Guidelines of this assignment are:

    Article summary: Your own summary – do not copy from an original source (1 page).
    Reflection: Your own discussion about the topic(s) of the article. Please apply your knowledge from this course and incorporate it into your discussion (1 page)
    Maximum pages: 2
    Font type and size: Times New Roman/Times, 12-point size, double spaced
    List of 3 reference(s)

What is “global temperature”?

How do you measure it?
What are the biases?

We covered several important figures from the IPCC report including global mean
temperature and its abrupt increase in recent years. When first published, such
temperature changes associated with atmospheric CO2 concentration increases
were eye-opening for most of us and raised strong awareness that something had to
be done about greenhouse gas emissions. At the same time, related scientific
findings were repeatedly targeted and attacked by politicians and lobbyists.

It is important for you to understand the “global mean temperature”, so that, in the
future, if and when you encounter the same question, you will have an answer with
a firm scientific foundation.

Let’s think about how we measure “global” temperature. Think about the
temperature variations you experience daily. How can we know what the ”global”
temperature is when we don’t even know exactly what our backyard temperature
is? Furthermore, different parts of Earth have varying temperatures: tropical versus
arctic, day time versus night time, bottom of a valley versus top of a mountain,
under your backyard tree versus sunny outdoor porch, etc. Are these varying
temperatures included in the “global” temperature? Even cities at same latitude do
not have same mean annual temperature. For instance, cites situated around 42N,
which include Springfield in MA, Chicago in IL, Norfolk in NE, Providence in RI. Do
these cities have same mean annual temperature?

No. Cities near the coast show a milder maritime climate, while intercontinental
cities such as Norfolk in Nebraska show greater temperature differences in day and
night/summer and winter.

Since there is great variety in temperatures, how do we obtain global temperature?

Please visit interactive website to plot global temperature anomalies from 1880 to 2020

How do you measure “global” temperature? How about CO2?
Is the world really warming?

Global mean temperature is the mean of direct temperature measured from all
over the world, including both land and sea. In other words, it is literary a mean of
as many possible measurements for as long as possible. That being said, the
number of direct measurements has changed significantly throughout time. We
had only a few temperature measurement stations in 1850 while we now have
thousands of measurements. With this, looking to the past, there was a greater
error margin in the earlier years (shaded colored area in the following figure).

As you have learned through previous lectures, especially during the glacial –
interglacial cycles, temperature change, measured through air bubbles preserved in
Greenland and Antarctic ice cores, coincide with CO2 concentration, as well as
other greenhouse gas concentrations. In recent years, direct measurement of CO2
concentration in the air has steadily increased since 1958 (Keeling Curve), which
coincides with recent increases in global mean temperatures.
(NOAA National Centers for Environmental information, Climate at a Glance: Global Time
Series, published March 2021, retrieved on April 8, 2021

Further reading:
Global Temperature Anomalies from 1880 to 2020, January 14, 2021
New Studies Increase Confidence in NASA’s Measure of Earth’s Temperature, May 23, 2019

Global Temperature Report for 2020

Global mean temperature needs to weight on some biases associated with the

temperature measurements. Specifically, as you see in this figure, land surface

temperature and sea surface temperature show different rates of increasing. Two

important biases to learn are associated with differences in land and ocean. First,

urban areas tend to heat up faster than rural areas that retain more moisture in

bare soil than in developed urban areas. Also, the ocean, as a body of water, has a

much greater heat capacity than the land surface, and can replace surface water

with colder deeper water (therefore, the ocean tends to be cooler than land

surface). In order to overcome such biases, scientists from different organizations

(Meteorological office Hadley Center and Climate Research Unit in UK, NOAA

National Centers for Environmental Information, and NASA Goddard Institute for

Space Studies) independently create global mean temperatures to verify that

they are reliable. All data and software used for the reconstruction of global

mean temperatures is available to the public.

Here is a relevant, useful and interesting web articles:

Further Reading
Are surface temperature records reliable?

Global Temperature Report for 2020

In Merchants of Doubts, Dr. Fred Singer stated: “In the last ten years, there

hasn’t been a warming. We don’t know why that is. But one doesn’t see any

warming in the observations. There simply is no trend.”

Is this really true? Let’s observe the data and comprehend what is going on.

The year of 2020 was reported to be the warmest year on record tied with

2016. Not only that, since the past 6 years were in the range of the warmest

years on record, scientist are now thinking that this increasing trend will

become the new norm.

Global Temperature Report for 2020

Global Temperature Report for 2020

Global temperature anomalies 2009-2013 (look at the north pole!)

Polar amplification is an important factor for cryosphere feedback. It is caused by
additional poleward energy transport, high-latitude water vapor content, and cloud

Also, it is important to remember polar amplification, which you learned in
previous lectures. Global temperature change does not occur evenly. Rather,
it shows preferential hot spots. the arctic region is one of them. Important
factors that cause such preferential warming in the polar region is cryosphere
climate feedback (Snow/ice-albedo feedback), cloud feedback, additional
poleward energy transport through wind and ocean, and the change in the
amount of water vapor at high-latitude.

Fig 5, IPCC Scientific Basis, WG1, Technical Summary: (Mann et al., GRL, 1999).

Northern Hemisphere Temperature record: Last 1000 years

This figure, originally published in 1999, is called the “Hockey Stick Curve” and has been

cited over 2300 times in peer reviewed journals by climate scientists and policy makers

(which is a significant number!). Particularly, the figure has made a broad audience

aware of acute changes in the Northern Hemisphere average temperature over the past

100 years. As climate studies are seeing greater importance, this paper has been a

target of dispute by climate skeptics specifically tied to the energy industry (e.g.

McIntyre and McKitrick 2003).

Original publication: Mann et al. 1999, Northern Hemisphere temperature during the
past millennium: inferences, uncertainties, and limitations


McIntyre and McKitrick 2003, Corrections to the Mann et. al. (1998) Proxy data base

and Northern Hemispheric average temperature series

How to explain global warming?

The question of Attribution

You learned about the evidence that proves anthropogenic climate change is
taking place. Now, let’s talk about how we explain the phenomena of global

Previously, you viewed this figure from the IPCC’s assessment report, showing
various factors that contribute to climate change. The next slide will include
further detail about each forcing component.

This figure is also from the IPCC’s assessment report. LOSU means ‘level of
scientific understanding’. In this figure, two different forcing components are
shown; anthropogenic and natural forcings. It is important to remember that
not only anthropogenic forcings, natural forcings also drive climate change. For
example, glacial/Interglacial cycles we observed from the ice core samples
earlier this semester that recorded atmospheric conditions over last 450,000
years are clearly caused by natural forcings as we, homo sapiens, did not exist
that time!

In this figure, each radiative forcing is associated with a value (watts per square
meter) quantifying how much each forcing contributes to climate change. Some
forcings have a negative number (contribute to cooling), whereas others have a
positive number (contribute to warming). The total net forcing is currently a
positive value. Thus, the climate trend is currently warming.

IPCC report

As shown in the previous figure, natural forcing can change climate. The
dominant energy source to change Earth’s climate, the sun, also varies its
energy emission. This figure shows natural changes in solar irradiance from
1874 to 1988. Solar irradiance is the amount of energy per unit area received
from the Sun. In recent decades, solar activity has been measured by satellites,
while before it was estimated using a proxy variation. Without satellite
observation, energy differences were too small to detect.

Solar irradiance is higher during a period called “solar maximum”, which
appears almost every 11 years. During a solar maximum, interesting features
that appears on the Sun’s surface…


Solar luminosity
Sunspot cycle (~11 year period,
~0.1% change in radiation


…are sunspots! Sunspots are relatively dark areas on the radiating surface of the
Sun, where intense magnetic activity inhibits convection and cools the
photosphere. Luminosity is the total amount of energy emitted by the Sun.

To summarize, more sunspot appears during a period of solar maximum, when the
Sun presents more intense magnetic activity (therefore higher luminosity).

Although solar irradiance was only recently measured by satellite, sunspots
have been observed for a very long time! The first such recording was made
by Galileo Galilei in the 17th century when he created the first telescope. In
addition, there are well documented historical records that captured solar
activity by Chinese astronomers. All records combined confirm the 11 year
cycle that coincide with a solar maximum.

Further reading:

During periods when there is active solar activity (more sunspots), scientists have
detected lower cosmic ray intensity on Earth; though a fraction of those rays,
short wave cosmic rays (high energy), are harmful to living organisms. The inverse
relationship between the number of sunspots and intensity of cosmic rays shown
in this figure explain that electro magnetic energy emitted by the Sun actually
shields such harmful cosmic rays.

The other important natural forcing that causes a climate response is volcanic
eruptions. In this figure from the IPCC report, you see changes in radiative forcings
between 1850 and 2000. The blue solid line shows strong negative forcing that
happens sporadically and coincides with significant historic volcanic eruptions.
When a volcanic eruptions is significantly large, it will eject large amounts of sulfur
dioxide into the stratosphere. This sulfur dioxide will eventually break down into
an aerosol form and, the stratosphere being very stable, will remain in the
stratosphere for up to few years; blocking sunlight that reaches the Earth’s
surface, and thereby decreasing temperature. Although this only has a short term
effect, up to few years, temperature drops can be significant and noticeable, and
such periods are called “volcanic winter”.

In this figure, abrupt decreases in volcanic radiative forcing are associated with
Krakatowa in 1883 (caused 5 year volcanic winter), Santa Maria in 1902, Mt. Pelee
in 1902 (caused casualties of 33000 people), Mt. St. Helens in 1980, El Chichon in
1982 (caused casualties of 3500 people), and Mt. Pinatubo in 1991 (largest
stratospheric disturbance since Krakatowa).

Hansen et al. 2005

This figure is a summary of climate forcings along with global temperatures from
1880 to 2000 published in the journal of Science.

Observed changes
consistent with:
þ expected responses

to forcings
Q inconsistent with

explanations (part of
a natural cycle)


All forcing


IPCC 4rth assessment report

Climate models are important tools for attributing and understanding climate
change. Understanding observed changes is based on our best
understanding of climate physics, as contained in simple to complex climate
models. For the 4th IPCC assessment report, you see observed global and
annual mean temperatures in black over the 20th century compared to the
temperature simulated by a wide range of climate models. On the top, in
red, individual model simulations are driven by external influences of both
anthropogenic and natural forcings, including changes in greenhouse
gases, aerosols, solar radiation and volcanic eruptions. These observations
rarely leave the range of those predicted by model simulations.

The lower figure compares the observed global and annual mean
temperature (in black) to the individual model simulations driven by only
natural forcings including changes in solar radiation and by volcanic
eruption (in blue).

To summarize, natural forcings cannot explain the temperature increase in
recent years without anthropogenic forcing!

The IPCC synthesis report for policymakers clearly states that the climate
system is warming and is largely influenced by anthropogenic causes.

IPCC Special Report on Global Warming of 1.5 ºC (2019)

And in 2019, the IPCC published a special report on Global Warming of 1.5 ºC.
Here is a quote from their statement providing quantitative values on how much
human activities have contributed to global warming.

“Human activities are estimated to have caused approximately 1.0�C of global
warming5 above pre-industrial levels, with a likely range of 0.8�C to 1.2�C.
Global warming is likely to reach 1.5�C between 2030 and 2052 if it continues
to increase at the current rate. (high confidence) ”

SPM Summary for Policymakers, p4

IPCC Special Report on Global Warming of 1.5 ºC (2019)

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