The
post asks only one question: when did CAGW begin? He takes us back half a million years and gives us something sadly lacking in the debate: long term perspective.
From wattsupwiththat.com
Here's the whole thing:
By WUWT regular “Just The Facts”
There have been a number of statements made recently about “Global
Warming Deniers”, e.g. “White House: Global Warming Deniers Wrong to
Reference Polar Vortex”
US News, “Watch The Daily Show mock Trump and other global warming deniers”
The Week and “Global warming denier Jim Inhofe: ‘Fewer and fewer’ senators believe in climate change ‘hoax’”.
The Raw Story
Given the apparent prevalence of “Global Warming Deniers”, it seems
prudent to take a look at the data so that everyone is clear when Global
Warming began and what is undeniable. As such, from the following EPICA
Dome C Ice Core record from
Vostok, Antarctica, over the last 450,000 years Earth has experienced numerous
Glacials, commonly referred to as
Ice Ages, and
Interglacials, like the
Holocene Interglacial we are experiencing today:
EssayWeb.net – Click the pic to view at source
“The
Last Glacial Maximum (LGM)
refers to a period in the Earth’s climate history when ice sheets were
at their maximum extension, between 26,500 and 19,000–20,000 years ago,
marking the peak of the last glacial period.” As such, one could argue
that Global Warming began about “19,000–20,000 years ago”.
However, there was “the Late Glacial Maximum (ca. 13,000-10,000 years
ago), or Tardiglacial (“Late Glacial”)” which was “defined primarily by
climates in the northern hemisphere warming substantially, causing a
process of accelerated deglaciation following the Last Glacial Maximum
(ca. 25,000-13,000 years ago)”. “As such, one could also argue that
Global Warming began about “13,000-10,000 years ago”.
Now looking at the
GISP2
Ice Core record from Greenland, over the last 10,700 years, you can see
the rapid warming that occurred at the end of last Glacial and that the
current Holocene Interglacial reached it’s maximum peak between 8000 –
7500 years ago:
climate4you.com – Ole Humlum – Professor, University of Oslo Department of Geosciences – Click the pic to view at source
Since the peak of the Holocene Intreglacial, Earth has experienced several additional descending peaks, including the
Minoan Warm Period between 3500 – 3000 years ago, the
Roman Warm Period between 2250 – 1500 years ago and the Medieval Warm Period between 1250 – 750 years ago. The
Medieval Warm Period and subsequent
Little Ice Age
can be seen clearly on the following temperature reconstruction based
upon Alexandre, 1987 and Lamb, 1988, found Page 250, Figure 7.1 of
IPCC Assessment Report 1:
JoNova – IPCC AR1 – Click the pic to view at source
The
Little Ice Age
“has been conventionally defined as a period extending from the
sixteenth to the nineteenth centuries, or alternatively, from about 1350
to about 1850, though climatologists and historians working with local
records no longer expect to agree on either the start or end dates of
this period, which varied according to local conditions. NASA defines
the term as a cold period between AD 1550 and 1850 and notes three
particularly cold intervals: one beginning about 1650, another about
1770, and the last in 1850, each separated by intervals of slight
warming.” As such, one could argue that Global Warming began in “about
1850″.
However, generally when referring to “Global Warming Deniers” there
is an implication that the “Global Warming” that’s being denied is
caused by anthropogenic carbon dioxide emissions. Anthropogenic CO2
emissions were de minimis in 1850. In fact, anthropogenic CO2 Emissions
from Fossil-Fuels did not become potentially consequential until
approximately 1950:
Carbon Dioxide Information Analysis Center – Click the pic to view at source
This is why the IPCC only claims to be;
“95% certain that humans are the “dominant cause” of global warming since the 1950s” BBC
As such, one could argue the Global Warming began in “the 1950s”.
However, if you look at the Met Office – Hadley Center HadCRUT4
Global Surface Temperature record for the last 163 years you can see
that temperatures didn’t warm during the 1950s, nor the 60s:
Met Office – Hadley Center – Click the pic to view at source
In fact it was not until approximately 1975 that temperatures began
to rise. As such, one could argue that Global Warming began
in approximately 1975.
However, in 2010 Phil Jones was asked by the
BBC,
“Do you agree that according to the global temperature record used by
the IPCC, the rates of global warming from 1860-1880, 1910-1940 and
1975-1998 were identical?” Phil Jones responded that,”Temperature data
for the period 1860-1880 are more uncertain, because of sparser
coverage, than for later periods in the 20th Century. The 1860-1880
period is also only 21 years in length. As for the two periods 1910-40
and 1975-1998 the warming rates are not statistically significantly
different. I have also included the trend over the period 1975 to 2009,
which has a very similar trend to the period 1975-1998. So, in answer to
the question, the warming rates for all 4 periods are similar and not
statistically significantly different from each other.”
The warming during the periods of “1860-1880″ and “1910-1940″, before
anthropogenic carbon dioxide emissions became potentially
consequential, is “not statistically significantly different” from the
warming during the periods “1975-1998″ and “1975 to 2009″. Thus there is
no indication that the warming between “1975-1998″ and “1975 to 2009″
is unnatural, unusual and/or caused by anthropogenic carbon dioxide
emissions. Global Warming may have started in 1975, but there is no
observable evidence [of] anthropogenic CO2 emission based Global Warming
began in 1975. As such, one could argue that anthropogenic CO2 emission
based Global Warming began sometime [after] 1975.
However, if you look at following UAH Satellite Lower Atmosphere graph for the last 34 years;
University of Alabama – Huntsville (UAH) – Dr. Roy Spencer – Click the pic to view at source
and this NASA GISS Mean Monthly Surface Temperature Anomaly graph for the last 17 years;
National
Aeronautics and Space Administration (NASA) Goddard Institute for Space
Studies (GISS) – Click the pic to view at source
you can see that Global Warming stopped in the late 1990s or early 2000s, which has been refereed to as “
The Pause” in Earth’s temperature. In fact, looking at the Werner Broznak’s recent
article, the Pause in each major temperature data set is as follows:
For
GISS, the slope is flat since July 2001 or 12 years, 6 months.
For
Hadcrut3, the slope is flat since July 1997 or 16 years, 6 months.
For
Hadcrut4, the slope is flat since December 2000 or 13 years, 1 month.
For
Hadsst3, the slope is flat since December 2000 or 13 years, 1 month.
For
UAH, the slope is flat since October 2004 or 9 years, 3 months. (goes to December using version 5.5)
For
RSS, the slope is flat since September 1996 or 17 years, 4 months.”
Shown graphically, that looks like this:
WoodForTrees.org – Paul Clark – Click the pic to view at source
As such, one could argue that for the last 17 – 9 years Global
Warming hasn’t been occurring, and thus Global Warming began in 1975 and
ended between 1996 and 2004.
However, this would not resolve the question of when the “Global
Warming” that’s being caused by anthropogenic Carbon Dioxide emissions
began. If you look at Global CO2 Emissions from Fossil-Fuels and;
EPA
– Carbon Dioxide Information Analysis Center, Oak Ridge National
Laboratory, U.S. Department of Energy – Click the pic to view at source
and Cumulative Anthropogenic CO2 Emissions from Fossil-Fuels, you can
see that emissions have been growing rapidly in the last few decades:
Carbon Dioxide Information Analysis Center – Click the pic to view at source
In fact the
Economist
noted in 2013 that “The world added roughly 100 billion tonnes of
carbon to the atmosphere between 2000 and 2010. That is about a quarter
of all the CO₂ put there by humanity since 1750. And yet, as James
Hansen, the head of NASA’s Goddard Institute for Space Studies,
observes, ‘the five-year mean global temperature has been flat for a
decade.’”
Thus, while anthropogenic CO2 emissions are the highest they’ve ever
been, and growing rapidly, Earth’s temperature has been in a 9 – 17 year
Pause. And the only period of warming that anthropogenic CO2 emissions
could have had a significant influence on, 1975 – 1998, is “similar and
not statistically significantly different from” the periods of 1860-1880
and 1910-1940 when there is no evidence of anthropogenic CO2 emission
influence. As such one could argue that “Global Warming” due to
anthropogenic Carbon Dioxide emissions may not have begun, that Earth’s
sensitivity to CO2 may be low, that natural processes may be large
enough to outweigh the effects of anthropogenic CO2 emissions, and/or
that preparing for a period of rapid and catastrophic Global Warming,
when there is no observational evidence that it is in fact occurring,
may be a historic folly.
Anyway, what do you think, when did Global Warming begin?
