Common ground in climate change
An article entitled Finding common ground amid climate controversy explored polarisation of opinion but noted that “climate change also offers tantalizing opportunities for finding common ground” (Kirk, 2018). The author cited the need for energy efficiency as “something few argue against” along with the general notions of stewardship of the planet. This post examines two areas of common ground underlying debates between those who believe that human activity is the main cause of climate change and those who believe that the cause is largely natural. The first area is scientific evidence and the second is uncertainty. The same evidence and the same measures of uncertainty can be used differently on opposite sides of the debate.
As an example, evidence of the past climate of Earth provided
by the science of paleoclimatology can be used to support both sides of the
argument. There is scientific evidence that earth’s climate showed large temperature
changes in the past, but also that temperatures were relatively low and stable during
most of humankind’s time on Earth. Opposite sides in a climate debate can find
themselves drawing selectively on the same common ground of science. Similarly,
regarding uncertainty, a probability figure close to one hundred percent can
give great confidence to one party but be dismissed by another as not amounting
to certainty.
Two main sections follow: Evidence from the past outlines
areas of common ground arising from paleoclimatology and other areas of
science, and Uncertainty concerns how we engage with information that is
less than 100% certain.
Evidence from the past
“Paleoclimatology uses a variety of proxy methods from Earth
and life sciences to obtain data previously preserved within rocks, sediments,
boreholes, ice sheets, tree rings, corals, shells, and microfossils” (Wikipedia
A, 2026). Proxy methods allow estimates of quantities such as past values of temperature,
precipitation, and CO2 levels which cannot be measured directly (McSweeney and
Hausfather, 2021).
Perhaps the most familiar climate proxy is annual tree rings,
whose thickness varies with conditions in the year of growth, and can provide climate
information for several centuries past. Other proxies can provide climate data
from millions of years ago: an example is certain seashells whose composition
varied depending on the temperature of the water in which they grew, and whose
age can be determined by techniques such as carbon-14 dating. These two methods
belong to the biological group of proxies, one of three main groups, the others
being chemical and physical. The composition of air trapped as bubbles in ice
cores is an example of a chemical proxy; and sediment layers in sea and lake
beds can provide physical proxies. Sediment accumulation can provide data on
conditions from millions to tens of millions of years ago and the earliest data
coming from sedimentary rocks extends to hundreds of millions of years.
A first skirmish
From the above brief outline of methods, it is possible to
see how a debate over whether present day climate change is or is not
anthropomorphic involves common ground. Both parties are likely to accept the science
underpinning paleoclimatology, but one party will see it as supporting the view
that present-day global warming is anthropomorphic in origin, while the other
would use it to oppose this conclusion. A graph used in a Smithsonian Magazine article
uses data from several sources to present a graph showing earth’s global
average surface temperature over the last 500 million years (Smithsonian, 2018).
It shows that relative to a base line in the 20th century, average temperatures
have sometimes been approximately 15 centigrade degrees higher, and at other
times approximately 6 centigrade degrees lower. It is easy to sympathise with
the view that the increase of a degree or two in recent years is just a natural
variation of little significance.
Evolution and agriculture
More common ground can be established if the parties agree that
Homo sapiens appeared relatively recently in geological terms. A Britannica (2026)
entry describes our species as “having originated in Africa more than 315,000
years ago”. Even allowing a generous margin of uncertainty on this figure, reference
to the Smithsonian temperature chart shows that Homo sapiens lived in a
relatively cool climatic period. Global average temperatures shown for the last
million years did not rise more than 3 centigrade degrees above the modern
baseline, and for much of that period earth was a few degrees cooler than at
present. The last peak of around 14 degrees higher than the present occurred
about 50 million years ago. The force of the argument that a rise in
temperature of around two degrees is insignificant in much weakened if we
confine attention to the period of existence of Homo sapiens.
The date at which sustained agriculture began has been
estimated as about 12,000 years ago (Wikipedia B, 2026). If this evidence
is accepted, the time span during which we need to consider Earth’s past
temperature is much reduced. The Smithsonian graph indicates relatively stable average
temperatures for this agricultural period, staying within plus and minus 2
centigrade degrees of the 20th century baseline. Agreement on the
time of appearance of Homo sapiens, and especially on when sustained
agriculture began, provides much better-defined common ground from which to
conduct a reasoned debate.
Temperature change, carbon dioxide and time
It would be possible for both parties to broadly accept the common
ground provided by paleoclimatology, the probable date for the arrival of Homo
sapiens, and evidence for the beginning of sustained agriculture provided by archaeology.
This might result in agreement that temperature increases of around 2 centigrade
degrees in modern times are a significant cause for concern, but it does not
settle the question of causation.
Paleoclimatology provides some information on the correlation
between past global average temperatures and atmospheric carbon dioxide, as
well as indicating their rates of change before there were humans on Earth.
“One of the most remarkable aspects of the paleoclimate
record is the strong correspondence between temperature and the concentration
of carbon dioxide in the atmosphere observed during the glacial cycles of the
past several hundred thousand years” (NOAA, 2021). This claim is supported by a
graph showing the close relationship between temperature and atmospheric CO2 in
parts per million against time over the past 800,000 years, but the article
warns that “the determination of cause and effect remains exceedingly difficult”
from the paleoclimatic record. A second article from the same organisation (NOAA,
2025) addresses the data from Antarctic ice core samples over the same 800,000
years. These “show CO2 fluctuating between roughly 180 ppm during ice ages and
300 ppm during warmer interglacial periods.” CO2 peaks never exceeded 300 ppm “until
the recent anthropogenic rise.” However, over the last 60 years “CO2 has
increased about 100 times faster than natural changes observed in the ice core
record” and reached over 422 ppm in 2024.
Natural causes
Some of the natural causes that are thought to affect
Earth’s temperature are changes in the sun’s radiation; changes in earth’s
orbit; volcanic activity; ocean cycles; or a combination of these effects.
However, the sun’s output can be measured, and the recorded changes are far too
small to account for the temperature increases that have occurred. Graphs of solar
radiance and Earth’s average surface temperature for the years 1980 to 2015 are
shown in “Causes of Climate Change” (EPA, 2025). The three components of Earth’s
orbital variation are described by Climate Change Academy (2025). The approximate
cycle times are 100,000 years for eccentricity, 41,000 years for tilt, and
26,000 years for precession. These times may be comparable with rate of glacial
change, but not with the present much more rapid temperature increase. Volcanic
eruptions produce both a heating effect from the CO2 they release and a cooling
effect from the aerosols that enter the atmosphere. Their effect lasts for only
a few years with the cooling effect predominant. Changes in ocean currents
affect local conditions, but do not change global average temperatures.
Combinations of radiance, orbit and volcanic actions are not enough to produce
the observed modern increase in temperature.
Uncertainty
Climate Change Denial was the title of an earlier
post which had sections on the psychology of denial, political elites, and climate
misinformation. Here the role of uncertainty will be briefly examined: it can
be seen as another area of common ground, different from that of science, and with
its own difficulties. Voltaire wrote that “Doubt is an uncomfortable condition,
but certainty is a ridiculous one”: many would agree with the first part of his
sentence, while finding the rest less easy to accept. It is natural to wish for
certainty, and hard, but necessary, to cope with doubt.
Mearns et al. (2025) open their discussion of uncertainty in
climate change with the above quotation from Voltaire. They borrow a definition
of uncertainty from the IPCC: uncertainty
is “a state of incomplete knowledge that can result from a lack of information
or from disagreement about what is known or even knowable.” They see this as
applying to the past, present and future, and describe uncertainty as a
combination of incomplete knowledge and the randomness of the real world. The
title of their open access book, Uncertainty in Climate Change Research: An
Integrated Approach, reflects the ways in which uncertainty can propagate
from one area of climate change to others. A few sentences from the book follow
to indicate its scope.
“Most mitigation and adaptation actions in a given
sector affect climate change-related risk in other sectors or interact with
mitigation and adaptation actions in other sectors”.
“With respect to future climate, we know temperatures and
sea levels will continue to rise, but we do not know by how much, by when, and
what path—sudden or smooth—the changes in climate will take.”
“The extent to which climate-related hazards affect
population health and health systems depends on various interacting
environmental, socioeconomic, and health factors and trends.”
“The goal of a climate-informed decision analysis is to
identify the optimal choice when climate un-certainty is a dominant factor
affecting the outcomes of the decision …”
Uncertainty must be quantified as far as possible, then accepted
and used in decision making. However, in some areas uncertainty is extremely
low, but nevertheless people still “deny even the strongest evidence and
distrust the scientific method”. This situation is addressed by Jylhä et al., 2023,
who refer to the common human goals of accurately understanding reality and causal
processes and predicting future events. Even conspiracy theories, despite
having “very little objective evidence to support them” are partly “motivated
by the desire to find some seemingly rational explanations” for events that individuals
seek to understand. The authors note that the public has “limited understanding
of some research topics and scientific principles and methodologies, and these
limitations provide a target for disinformation campaigns.” The difficulty that
many of us have in understanding uncertainty may be one of the prime targets for
such campaigns.
References
Britannica, 2026, Homo sapiens, online, accessed 8 August
2026
https://www.britannica.com/topic/Homo-sapiens
Climate Change Academy, 2025, Understanding Natural Drivers
of Climate Change: Solar Variability, Orbital Shifts, and More, online,
accessed 8 August 2026
EPA, 2025, Causes of Climate Change, U.S. Environmental
Protection Agency, online, accessed 8 August 2026
https://www.epa.gov/climatechange-science/causes-climate-change
Jylhä, K., et al., 2023, Science Denial: A Narrative
Review and Recommendations for Future Research and Practice, 2023, European
Psychologist, online, accessed 18 September 2026
https://psycnet.apa.org/fulltext/2023-30588-001.html
Kirk, K., 2018, Finding common ground amid climate
controversy, Yale Climate Connections, online, accessed 5 August 2026
https://yaleclimateconnections.org/2018/04/finding-common-ground-amid-climate-controversy/
McSweeney and Hausfather, 2021, Mapped: How ‘proxy’ data
reveals the climate of the Earth’s distant past, Carbon Brief, online, accessed
5 August 2026
https://interactive.carbonbrief.org/how-proxy-data-reveals-climate-of-earths-distant-past/index.html
Mearns L. et al., Eds., 2025, Uncertainty in Climate
Change Research: An Integrated Approach, Springer, Cham, open access book,
online, accessed 8 August 2026
https://link.springer.com/book/10.1007/978-3-031-85542-9
NOAA, 2021, Temperature Change and Carbon Dioxide Change US
Department of Commerce, online, accessed 8 August 2026
NOAA, 2025, Carbon Dioxide over 800,000 years, US Department
of Commerce, online, accessed 7 August 2026
https://www.climate.gov/media/16929
Smithsonian, 2018, Here’s How Scientists Reconstruct Earth’s
Past Climates, Smithsonian Magazine, online, accessed 5 August 2026
Wikipedia A, 2026, Paleoclimatology, online, accessed 5
August 2026
https://en.wikipedia.org/wiki/Paleoclimatology
Wikipedia B, 2026, History of agriculture, online, accessed
8 August 2026
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