A known as a global warming pause or slowdown;

A global warming
hiatus, is a period of relatively little change in globally averaged surface
temperatures, also known as a global warming pause or slowdown; climate is
classically averaged over a 30-year period. The apparent slowdown in the
increasing global surface temperature is what it is referred to as a ‘hiatus’,
including the changes also in radiative force, deep ocean heat uptake and
atmospheric circulation changes.

The
Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report
concluded that the global surface temperature “has shown a much smaller
increasing linear trend over the past 15 years in 2012 than over the past 30 to
60 years.” It showed that between
the years of 1998 and 2012, the surface of earth experienced very little
warming. This recent decadal slowdown is unique in having occurred during a
time of strongly increasing anthropogenic radiative forcing in our climate. Also
the same time that political negotiations for preventing climate change
occurred. This trend phenomenon, caused the public to doubt about how well
anthropogenic climate change and natural variability were understood. This
caused suspicion of residual data bias to mute global warming and possible
thoughts of tampering with data shown to show most preferable results.

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The
fifth report showing global mean surface temperature (GMST) in the 14 years after 1998 known as the ‘hiatus’, has caused
discussion to the evidence of proving if there was in fact a hiatus, depending
on the period and definition. Some of the main definitions used to characterize
a hiatus are when the trend in GMST is zero,
negative or not significantly positive and if the estimated trend shown in observations
appears lower than that of the existing long-term warming trend and model
simulations. There have been many different
perspectives on the hiatus which all have different techniques to collect datasets,
each with variations as methods get updated with further knowledge and advanced
technology.

The reasons concerning the
hiatus include factors such as; external drivers, the earth’s climate response
to CO2 and other radiative forcing, and internal variability, all
which affect the GMST. They explain both the magnitude of the GMST and its
spatial pattern relative to what was projected from model simulations. The internal variability factor is affected by the choice
of the hiatus’s beginning with the IPCC report observations starting in 1998,
an extremely warm El Niño year. In the El
Niño years, the sea surface temperatures (SST) in the tropical Pacific
increase, leading to increased heat loss from the ocean to the atmosphere; the
heat is transported to higher latitudes by the atmosphere, leaving a large surface
area of the earth warmer than normal. This time period which the hiatus is
measured in, experiences more heat entering the climate system than that
leaving at the top of the atmosphere; suggesting the climate system has warmed
as a whole and did not slowdown like the hiatus may suggest.

The two hottest years on
record, 2015 and 2016, highlighted the question if ‘global warming has stopped’
to the public, one that the scientific community has been facing for many
years. To confirm if there was a hiatus or global warming slowdown at some point
is still in debate, with some arguing strongly for it. Warming in 2014 and the
record temperature in 2015 illustrate the sensitivity of estimates and the
choice of trend length. To better portray the trend defining the hiatus with set
start and end dates, overlapping windows can be used and should be selected
based on the physical understanding of ?F, the estimate of anthropogenic
radiative forcing involved.

In the ‘ScienceMag’ article, it
strongly disagrees with the data reported by the IPCC. It suggests that global
surface temperature trends are higher than the reported in the IPCC fifth
assessment report, particularly concentrating on the recent years gone, and the
suggested estimate for the rate of warming during the first 15 years of the
twenty first century which is as great as the last half of the twentieth century
and has also been considerably less than the average simulated rate in the
global-average surface temperature anomaly. These results do not support
evidence for a hiatus in the increasing of global surface temperature.

Evidence for these conclusions sources
from the argument that observation methods are always changing, as new methods
and technologies advance, the data collection techniques will all differ, but
these different methods are needed in different environments. Addressing these
particular issues shows how the measuring of global warming can be inaccurate
and manipulated for preferred results due to the varying results in different
techniques; this has led to discussion on how accurate the data reviled is.

Positive
conclusions that resulted from the investigation into the hiatus; from the data
collected by the IPCC, it can be seen that the GMST results correlate with
previous findings of a reduced rate of surface warming during years, 2001–2014,
a time period in which anthropogenic forcing increased at a relatively constant
rate. Due to this, scientific research has a more advanced understanding and
better ability to explain temperature variations and the influence of
uncertainty in ocean SSTs on decadal timescale GMST trends, including those
experienced during the early twenty first century.

Contradictory conclusions
stem from different definitions of ‘hiatus’ and from different datasets. There
is much debate from multiple sources, whether the hiatus occurred or not is
thought to depend on the time period considered, and which dataset and the
hypothesis tested, including the changes in forcing, ocean heat uptake, natural
variability and incomplete observational coverage. Consequently, the diverging
conclusions do not need to be inconsistent and there is no strong contradiction
between studies that claim that the hiatus did not occur and others that claim that it
did.

To summarise, one of the
challenges that arises for the scientific community is the pressure from the
public, and to keep engaged in fast-paced communication, science requires time
to analyse, test hypotheses and publish results for these situations. Investigation
into the hiatus has been enabled mostly by prior research, and represents an
important scientific effort to quantify the climate signals associated with natural
external forcing, internal variability, and anthropogenic factors. This combined
with recent stronger warming trends, it is a more confident opinion that human
influence is dominant in long-term warming.