Climate Science: A Simple Guide

Climate science looks at long term weather patterns that have established themselves now, or will do in the future. Its cousin, paleoclimatology, looks at ancient climates. In this article we take a quick look at how climate data is collected, how the data is modelled using computers, and how the climate denial movement rejects mainstream climate science.
Climate Science Guide
Image: ESA.

Climatology Involves Different Disciplines

Climate science, also known as climatology, investigates how Earth’s climate system works. It aims to understand how global and local climates occur as well as the processes that cause them to change.

In doing this, it relies on a wide range of ideas and measurements from many different disciplines, including meteorology, oceanography, atmospheric physics and chemistry, volcanology, geology, pedology, glaciology, microbiology and more. This scientific data also helps scientists to develop more accurate climate models, which have become a critical component of all climate research. 1

Climate science emerged as a distinct area of study during the second half of the 20th century. Although often called “climatology”, it is very different from the field of climatology that existed before. That earlier climatology, which existed from the late-nineteenth century onwards (if not earlier), was an inductive science, which sought to infer general laws from specific observations. By the mid-20th century, it had become focused on the production of statistics from weather observations.

By contrast, climate science seeks to understand and predict the Planet’s climate – involving continents, oceans, ice sheets, atmosphere, paleoclimatology, and more – and it takes full advantage of digital technologies to simulate the large-scale interactions between air, sea and land, which transport heat, moisture, matter and other stuff that combine to create the basic climate variables, like surface temperature and rainfall.

Climate science is inevitably driven by (and financed by) the pressing need to understand and forestall man-made climate change, caused by the accumulation of carbon dioxide and other heat-trapping gases in the lower atmosphere. But it’s not true to say that climate science is merely the study of human-induced global warming or extreme weather events like hurricanes and droughts.

The truth is, many climate scientists work on fundamental issues such as how energy flows in the system, how certain physical processes influence climate, how climate feedbacks differ from climate forcings, about how Earth’s climate system compensates for and offsets any excesses (of temperature, water vapor, carbon dioxide) that arise, and much more.

Climate science also aims to ascertain how climate might change in the future if greenhouse gas emissions and other anthropogenic forcings were to evolve in certain ways. Such predictions and the policy options to be inferred from them, is of paramount interest to policy makers. For more, see: Our Climate Plan Can’t Cope.

Main Influences On Climate

Earth’s climate is regulated by a planet-wide system involving the air (atmosphere), the oceans (hydrosphere), the polar ice sheets (cryosphere), the soil (pedosphere), the rocks beneath it (lithosphere), and all living organisms (biosphere). Human activities are also included, such as those that release carbon dioxide (CO2) into the atmosphere, and those – like deforestation – that upset the natural carbon cycle and water cycle maintained by the Amazon rainforest.

That said, climate scientists tend to classify human action as an external influence – on a par with variations in the amount of sunlight received, or volcanic eruptions. From a philosophical viewpoint, treating human activity as something external to the climate system may reflect a deep ambivalence about whether humans are part of nature, but in fact it’s perfectly consistent with the idea that human actions are the product of political values, which are completely separate from the earth sciences.

Mercifully, despite some notable attempts 2 both climate science and climate change have remained relatively free of philosophical discussion. Political discussion, however, lies at the very heart of these areas.

Climate Data

Climate researchers employ numerous sources and types of data, including observations from satellites, aeroplanes, drones, balloons and other remote monitors, as well as ocean buoys and ships. On land, data comes from land stations, as well as ice cores, tree rings and lake sediments, and the like. 

Ice core sample taken from West Antarctica. Ice cores are invaluable for paleoclimatology.
An ice core taken from West Antarctica. Paleoclimatologists – scientists who study Earth’s earlier climates – collect evidence from glaciers and polar ice sheets by drilling deep down into the ice. The samples they collect – called ice cores – contain a physical record of what our climate was like hundreds of thousands of years ago. The dark band in this ice core is the remains of a layer of volcanic ash that settled on the ice sheet approximately 21,000 years ago. Image: Heidi Roop, National Science Foundation (NSF)

Important contributions to the collection of temperature data have come in particular from NASA’s Goddard Institute for Space Studies (GISS), the U.S. National Centers for Environmental Information (NCEI), the University of East Anglia’s Climatic Research Unit (CRU), and the non-governmental organization Berkeley Earth. All four have, incidentally, confirmed the leading role of the man-made greenhouse effect in the rise of global warming.

But even using this wide variety of sources, together with the latest computer models, the sheer scale and complexity of the global climate system continues to defy attempts to understand it. And so far, the computing power needed to simulate worldwide climate changes remains well out of reach.

For example, take the relationship between concentrations of greenhouse gases and average sea-level. In one study, researchers at the National Oceanography Centre, Southampton, compared pairs of CO2 level/sea-level measurements from the past 40 million years. They found that greenhouse gas concentrations similar to the present (400 parts per million) were associated with sea levels at least nine meters (29 feet) above current levels. 3

So, does this mean that a sea level rise of nine meters is imminent? Probably, say scientists. But they have no idea when, exactly, or what will happen if we reduce emissions in the meantime. There are simply too many variables for current computer models to handle.

Paleoclimate Studies

Climate researchers also study climates of the past, that occurred before the advent of meteorological instruments. These paleoclimatic studies rely on “climate proxies”: physical evidence of past climates, such as variations in the different isotopes of oxygen in ice cores from Antarctica, or in the remains of marine organisms found in marine sediments. 4 Other climate proxies come from lake sediments, tree rings, corals, and other sources. 5

Establishing the validity of proxy-based paleoclimate reconstructions is not easy. To begin with, tree rings can be affected by temperature, precipitation, soil quality, cloud cover, and the like, which makes it difficult to calculate or infer a single variable of interest, such as CO2 level or temperature. Second, proxies may have limited geographical relevance. 6 See also our article: When did Global Warming Start?

Types Of Climate Models

Models of the climate system capable of replicating various climate pathways or scenarios have become vital to both theoretical and applied research.

The complexity of climate models varies according to several factors. They include: how many spatial dimensions are represented; how closely those dimensions are represented; how many components and processes are included in the model; how realistic the representation of those processes is. Not surprisingly, the more complex the model, the more computer power is needed.

Moving beyond the simplest types – the energy balance models (EBMs) – as well as Earth system models of intermediate complexity (EMICs) – we reach the highly complex general circulation models (GCMs), which replicate interactions between the atmosphere and oceans in three spatial dimensions. They also include representations of sea ice as well as the land surface. The most recent climate models – earth system models (ESMs) – incorporate additional components concerning atmospheric chemistry, aerosols and/or ocean biogeochemistry. Despite these advances, simulating a number of key processes like the formation of clouds, remains a major challenge. (See also: How do Clouds Affect Climate?)

Another variant is the regional climate model (RCM). Similar to GCMs and ESMs, RCMs are designed to produce realistic, theory-based representations of climate system processes. However, unlike GCMs and ESMs, RCMs simulate only a portion of the globe (like a continent), which enables them to produce a higher spatiotemporal resolution. This allows them to simulate smaller-scale processes in great detail.

Climate Modeling

A few dozen GCMs/ESMs are operational at certain modeling centers around the world. 7 Some employ over 1 million lines of computer code, requiring considerable expertise to set up and run.

These machines typically comprise several different models, each corresponding to different parts of the climate system: atmosphere, ocean, land surface, sea ice, and so on. For example, the Community Earth System Model version 1.2 (CESM1.2) housed at the U.S. National Center for Atmospheric Research incorporates the Community Atmosphere Model (CAM) and an extension of the Parallel Ocean Program (POP). In addition to the differing models, these machines also have a “coupler” that conveys information from one model to another. In effect, the Coupler is a communications hub that connects the differing models.

What is the role of social and ethical values in climate models? One study contends that such values definitely influence climate model construction (and therefore outcomes) by determining priorities in model development. Researchers argue that social and ethical principles come into play whenever there are no knowledge-based reasons for deeming one model-building option to be the optimum. 7 Another paper proposes that social and ethical value judgments are a legitimate influence on climate model construction when this promotes democratically-endorsed social and epistemic aims of research. 8

Climate models are used in the search for scientific explanations and understanding. Like, ‘what elements of the climate system cause climate change?’ In addition, climate models are employed to test and make predictions, especially long-term conditional predictions, known as projections. The best-known such projections are the four “Representative Concentration Pathways” outlined in the IPCC’s Fifth Assessment Report. 9 Each scenario is based on specific greenhouse gas emissions and varying climate change mitigation strategies.

Questions and Answers About Earth’s Warming
For more than 100 popular questions and answers on all aspects of our climate crisis, see: 50 FAQs About Global Warming and 50 Climate Change FAQs.

Evaluation Of Climate Models

The evaluation of climate models tends to focus mainly on describing the extent to which their results accord with observations and on how this has improved from one generation of models to the next. For example, recent IPCC reports conclude that current models provide “credible quantitative estimates” of climate system conditions in support of climate change detection, attribution and projection. Even so, the expected accuracy of modeling results in these three areas is hardly ever quantified. To move the discussion forward, one study outlines a conceptual framework for the evaluation of climate model accuracy for particular purposes. 10

Anthropogenic Climate Change

In 1988, following arguments as to whether or to what extent man-made global warming was a possibility, climate scientist James Hansen famously testified to the U.S. Congress that global warming was already happening. The same year, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) founded the Intergovernmental Panel on Climate Change (IPCC). Its initial brief was to prepare a set of recommendations for a future conference on climate warming – a conference which became the United Nations Framework Convention on Climate Change (UNFCCC). The IPCC does no independent research, instead it draws on the latest peer-reviewed studies and other expertise of the international climate science community.

The IPCC’s Fifth Assessment Report concluded that it is “virtually certain” (with a probability of 99%) that the increase in Earth’s temperature since 1950, is not due to internal variability alone. It also concluded that it is “extremely likely” (with a probability of 95%) that over half the global warming since 1950 was due to man-made greenhouse gas emissions and other man-made climate forcings. 11

In its Special Report on Global Warming of 1.5°C (2018) the IPCC stated that human activities are estimated to have caused roughly 1.0°C of global warming above pre-industrial levels, with a likely range of 0.8°C to 1.2°C. 12

How much scientific consensus is there on the attribution of climate change? It is often said, for example, that 97 percent (or more) of climate scientists agree that climate change is man-made. 13

But this focus on consensus is actually irrelevant. What counts is that there is hard evidence for a scientific claim, not whether a certain percentage of scientists endorses it. Even so, consensus among specialists can serve as indirect evidence for a scientific claim.

Climate Denial And Associated Controversies

Climate contrarians dispute key conclusions of mainstream climate science, via a host of public platforms, such as blogs, newspaper op-ed pieces, media interviews, Congressional hearings and, less often, scientific journals.

These deniers come in many shapes and sizes, but the most dangerous ones are the right-wing groups and fossil fuel companies who run the climate change denial machine, whose aim is to block climate action by manufacturing doubt about the reality of anthropogenic climate change.

Controversies manufactured or stirred up by contrarians include: (a) The tropospheric temperature controversy. (b) The hockey stick controversy. (c) The climategate controversy. (d) The hiatus controversy. With the exception of (c) which uncovered a lack of transparency in explanations furnished by certain climate scientists, all have been satisfactorily explained, although the arguments continue.

Contrarian denial and dissent has affected climate science in several ways. For a start, research is sometimes aimed at rebutting contrarian claims and arguments. In addition, pressure from contrarians allied to the fear of being labelled “alarmist” may account for climate scientists’ tendency to err on the side of caution in their forecasts.

Some experts argue that contrarian activities have retarded scientific progress in at least two ways: (a) by making scientists respond to an apparently endless series of unnecessary objections and (b) by creating a hostile atmosphere in which some scientists are afraid to address certain topics, or to defend their ideas as robustly as they believe is appropriate.

They argue that, although dissent in science in general, and climate science in particular, frequently adds to our knowledge, the denials and dissent voiced by climate contrarians has tended to adversely affect scientific knowledge. 14

NASA weather satellite. An essential tool in climate science.
NASA satellite from one of their Earth Observation missions. The satellite tracks and monitors vital climate change, weather and pollution indicators. Photo: © NASA/Expedition 31, CC BY-NC-ND 2.0

Ethics And Climate Change

When it comes to the ethics of climate change, the big question is: What should be done about man-made global warming, and by whom?

The question is important because the effects of global warming are already impacting on ecosystems and their species, just as the effects of global warming on humans are becoming all too apparent, and look like worsening rapidly. 15

Unfortunately, when we attempt to answer the question, we are immediately snared in further questions relating to what is fair as between nations and also as between the old and young. In addition, there are questions concerning our ethical obligations to animals.

For example: (a) Do states that have emitted large quantities of greenhouse gases in the past, have an obligation to pay more of the costs of climate action than other nations? 16 (b) When planning climate mitigation, how should the interests of future generations be weighed against those of today’s generations? (c) What weight should be attached to the interests of animals and other organisms, when deciding on climate action? 17

These ethical issues are critical when it comes to deciding (1) Who should pay for the costs of climate action? (2) How should these costs be financed?

Atmospheric Chemistry
Draws on climatology, environmental chemistry, meteorology, computer modeling, oceanography, volcanology and other disciplines.

Atmospheric Physics
The physics of the atmosphere, scattering theory, wave propagation models, cloud physics, spatial statistics.

Climatic Geomorphology
Part of historical geology, it involves the study of the role of climate in shaping landforms and other terrestrial processes.

The study of snow and ice. A central area of climate science.

Interactions among organisms and their biophysical environment.

The science of living things.

The study of rocks, and the processes which cause them to change.

The physics of the Earth and its environment in space.

The scientific study of ice and glaciers.

Falls under the atmospheric sciences. Includes atmospheric physics and atmospheric chemistry, but focuses on weather forecasting.

The study of microscopic living organisms.

The study of the world’s oceans, their chemical properties, origin and geology, and living organisms – a critical area for climate science.

Reconstructs earlier climates by examining historical data found in ice cores and tree rings (dendroclimatology).

The scientific study of prehistoric fossils.

Uses prehistoric data from ice cores and tree rings to determine hurricane behaviors over millennia.

The study of soils in their natural environment.

The study of natural sediments how they are formed.

The study of volcanoes, lava, magma and associated phenomena.


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