Weather and climate conditions are continually changing in different parts of Earth. The natural process known scientifically as climate variability produces variations in the average state of atmospheric variables such as temperature and precipitation across spatial and temporal scales beyond individual weather events. When changes persist and systematically alter the mean characteristics of climatic variables over periods longer than about a decade, they are described as climate change. Climate change can arise from natural processes or human activities. However, researchers attribute the dominant cause of the present era of climate change to human industrial activity.
 |
| Image from the original article |
Earth's energy budget
Earth and its atmospheric system receive nearly all their energy from the Sun. Under normal conditions, a substantial portion of incoming energy is reflected back to space either before entering deeply into the atmosphere or after interacting with the atmosphere and surface.
Greenhouse gases such as carbon dioxide interact with outgoing infrared radiation, retaining energy within the atmosphere–ocean system and redistributing it through Earth's climate system. The balance among incoming solar energy, outgoing energy, and internal redistribution is commonly described as Earth's energy budget.
The climatological view is that human activity—particularly the release of unprecedented quantities of greenhouse gases—has disturbed this balance by reducing the proportion of energy escaping to space relative to the energy entering the Earth system.
Evidence connecting human activity and greenhouse gases
A NASA study published in 2014 presents as direct supporting evidence for the human role in contemporary warming. The study modelled the distribution of greenhouse gases, including carbon dioxide, whose atmospheric concentration varies seasonally.
The NASA modelling showed that major emission sources were concentrated in areas of high human activity and population density. Because a larger share of the world's population and industrial activity is located in the Northern Hemisphere, the modelled emission sources were concentrated there. After release, greenhouse gases gradually spread through the Northern Hemisphere atmosphere and subsequently into the Southern Hemisphere.
The annual cycle of atmospheric carbon dioxide in the model also reflected the strong concentration of anthropogenic emission sources in the Northern Hemisphere. This spatial and seasonal behaviour is an evidence supporting the scientific attribution of contemporary climate change to human activities.
The rate of change matters
Climate itself has always changed. The central concern is the speed and rate of the present changes. Past mass extinctions are invoked to illustrate how rapid climatic disruption can overwhelm the ability of biological species and ecosystems to adapt.
There are two broader observations. First, humans may possess considerable adaptive capacity, but economic structures and inequalities can affect how quickly different societies and groups are able to adapt. There is a critical view of the role of capital and economic-growth priorities in that process.
Second, substantial research in industrialized countries was already examining how adaptation could be achieved. Continued reliance on fossil fuels, the author argues, raises the eventual cost and difficulty of adaptation. We cannot assume that existing knowledge alone will allow humanity to adapt successfully to every consequence of rapidly changing climate conditions.