17.1: Note on Usage

Weather vs. Climate

Climate is not weather, and weather is not climate. However, you may have heard these related terms used interchangeably, so parsing their precise meanings is a good place to begin this story.

Following the definitions used by the National Oceanographic and Atmospheric Administration (NOAA), we should think of weather as short-term atmospheric conditions in a particular place, at a particular time. Climate, by contrast, can be best understood as a statistical pattern describing much longer time periods over larger regions, and involving a greater number of factors, including the variations of Earth’s orbit and resulting fluctuations in ice ages and interglacial periods.

A single hurricane is weather. A pattern of hurricanes over many decades is climate.

As you have probably experienced, the weather forecast for an individual day can turn out to be quite inaccurate; in the morning you were assured there was no need for an umbrella, by the afternoon you are soaking wet from rain. Weather forecasts beyond one day become increasingly uncertain; the outer range of published forecasts is usually about ten days. This inability to predict weather, despite excellent data about real-time conditions and powerful computer models, is a function of the branch of science known as chaos theory, which mathematically describes limitations in systems in which very small changes in initial conditions produce very different results. Under the limitations of chaos theory, if there is an almost-unmeasurably small change in humidity or wind speed then that day’s weather forecast becomes inaccurate. What chaos theory informs us is that we are simply never going to be able to predict long-term weather, not because of a lack of information or problems with computer models, but because of the laws of nature.

Those who deny the reality of climate change frequently cite this inability to predict short-term weather as an indicator that long-term climate predictions must also be suspect. This claim is without scientific merit, but it reinforces the importance of correctly distinguishing weather and climate. A related intentional misrepresentation of the difference between weather and climate posits that cold winters refute the idea of a warming world.

Climate, in contrast to weather, is highly predictable. We know that through statistical analysis over years of data, summers will tend to be hotter than winters, and winters cooler than summers, and we can moreover discern trends in the lengths and timings and intensities of these patterns. We know that hurricanes and tornadoes tend to be concentrated in certain months, but are virtually unknown in other months. We know that the changes in the concentrations of certain gases in the atmosphere, such as CO₂ (carbon dioxide) and CH₄ (methane), can exert a powerful forcing on the temperature of the atmosphere.

Forcings/Responses

Climate forcing is an important concept to understand. Forcings push climate in complicated directions and create responses. Many things can act as a forcing, including greenhouse gases and particles released from volcanoes; for example, the 1991 eruption of Mt. Pinatubo in the Philippines released so much sulfur dioxide that worldwide temperatures responded with lowered temperatures for two years. Another forcing is the orbital variations known as Milankovitch Cycles, which are linked to ice ages and interglacial periods. Changes in solar radiation–the intensity of sunlight–can also be a climate forcing. And, of course, in the current world the most important forcing of all is the prodigious amount of anthropogenic greenhouse gases, such as CO₂ and CH₄. (Anthropogenic means human-caused.) Of these anthropogenic greenhouse gases, carbon dioxide is currently responsible for the greatest forcing, though the influence of methane is rising.

Radiative Forcing

Radiative forcing refers to the difference between incoming and outgoing energy (see Figure \(\PageIndex{1}\)). If the Earth were in balance–not getting hotter or colder–then the radiative forcing would be zero. If radiative forcing is positive, this indicates a warming world, and if negative, a cooling world. We are currently in the situation where more radiation accumulates on Earth than leaves Earth.

Figure \(\PageIndex{1}\): A diagram of solar radiation and energy inputs and outputs, titled "Net energy imbalance = energy in - energy out." This diagram shows the imbalance in sources heating from radiation versus infrared radiation responsible for cooling the planet. "Net energy imbalance" by Janelle Christensen, USDA is in the public domain. Access a detailed description.

If we choose the year 1750 (before the onset of the Industrial Revolution) as a baseline of 0.0 radiative forcing, then by 1950 the radiative forcing rose to 0.57 watts per square meter. (To understand the units of watts per square meter, think of a solar panel–how much electricity does a square meter solar panel produce?) By 1980, this radiative forcing rose to 1.25 W/m². By 2011, 2.29 W/m². And by 2019, 2.72 W/m². This rise in this radiative forcing speaks to an accelerating heating imbalance for our warming planet; anthropogenic greenhouse gases create this imbalance.

The understanding of climate forcings/responses is superior to simple cause/effect models. In a naive cause/effect model, one change in one place produces a proportional change elsewhere. Complicated, dynamic climate systems require a more informed approach. For example, we might posit that as CO₂ levels rise, all ocean temperatures will also rise in lockstep; however, in reality due to increased ice melting, some oceanic areas near Greenland are actually cooling as this frigid water–recently glacial ice–surges into the surrounding seas. We might imagine that as humans pump CH₄ into the atmosphere, the resulting rising temperatures will produce droughts; however, higher temperatures also exponentially increase the ability of the atmosphere to hold evaporated water, so some intense storms will actually be wetter, causing increased flooding events. This leads to the seeming contradiction that climate change enhances both droughts and floods. How can it be both? This is the reality of complicated forcing/response systems. Climate is inherently multifaceted, requiring more than a naive model of cause and effect. Climate forcing/response is the way to think about these factors.

Climate Change vs. Global Warming

On a final usage note, this book uses the term climate change rather than global warming. One problem with the older term global warming is that while the majority of the planet suffers from increasing heat due to anthropogenic forcings, some areas may experience cooling (recall the aforementioned cold waters near Greenland). Such exceptions will be pounced upon by well-funded, well-organized anti-scientific campaigns to deny the reality of climate change. The term climate change, by contrast, implies a weirding of climate–strange conditions, potentially both warmer and colder, drier and wetter. It is this stochastic destabilization of climate that so concerns scientists.

Query \(\PageIndex{1}\)

Query \(\PageIndex{2}\)

Query \(\PageIndex{3}\)

References

1. Satterfield, D. (2011, January 24). Rebuttal to 'Scientist's Can't Even Predict The Weather Right'. Retrieved September 29, 2023, from https://skepticalscience.com/global-warming-cold-weather.htm
2. Mason, J. (2023, September 3). Does cold weather disprove global warming? Retrieved September 29, 2023, from https://skepticalscience.com/global-warming-cold-weather.htm
3. IPCC, 2021: Chapter 7, Figure 7.6. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Forster, P., T. Storelvmo, K. Armour, W. Collins, J.-L. Dufresne, D. Frame, D.J. Lunt, T. Mauritsen, M.D. Palmer, M. Watanabe, M. Wild, and H. Zhang, 2021: The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 923–1054, doi: 10.1017/9781009157896.009 .] https://www.ipcc.ch/report/ar6/wg1/figures/chapter-7/figure-7-6