Friday, March 29th, 2024

Climate Change News: Was the Earth already warming or did global warming reverse the cooling trend? know what is the truth


Arizona: Over the past century, Earth’s average temperature has risen rapidly by about one degree Celsius (1.8 degrees Fahrenheit). It is difficult to dispute the evidence. It comes from thermometers and other sensors around the world. But what happened thousands of years before the Industrial Revolution, before thermometers, and before humans warmed the climate by releasing heat-trapping carbon dioxide from fossil fuels? At that time, was the Earth’s temperature warming or cooling? Even though scientists know more about the most recent 6,000 years than about any other multimillennial interval, studies on this long-term global temperature trend draw contrary conclusions.

Many samples of the earth were analyzed
To try to resolve the gap, we conducted a comprehensive, global-scale assessment of the existing evidence, including both natural archives, such as tree rings and seafloor sediments, and climate models. Our results, which were published on February 15, 2023, suggest ways to improve climate forecasting while avoiding missing some important slow-moving, natural climate feedbacks.

Learn about Global Warming
Scientists like us who study the climate of the past, or palaeoclimate, look for temperature data from thermometers and satellites from much earlier times. We have two options: we can obtain information about past climate stored in natural archives, or we can simulate the past using climate models.

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There are many natural records that record changes in climate over time. Annual growth rings in trees, stalagmites and corals can be used to reconstruct past temperatures. Similar data can be found in small circles found in glacier ice and in sediments that have formed over time at the bottom of oceans or lakes. These act as substitutes or proxies for thermometer-based measurements. For example, changes in the width of tree rings can record fluctuations in temperature. If temperatures are too cold during the growing season, the tree ring formed that year is thinner than in a year with warmer temperatures.

Earth’s infinite secrets are hidden in sea sediments
Another temperature estimate is found in ocean floor sediments, in the remains of tiny ocean-dwelling organisms called foraminifera. When a foraminifer is alive, the chemical composition of its shell changes depending on the temperature of the ocean. When it dies, the shell sinks and over time is buried by other debris, forming layers of sediment on the ocean floor. Paleoclimatologists can then extract sediment cores and chemically analyze seeps in those layers to determine their composition and age, sometimes for millennia.

Another tool we have for exploring the past climate is the climate model, which is a mathematical representation of Earth’s climate system. They model the relationship between the atmosphere, biosphere and hydrosphere in order to get as close to reality as possible. Climate models are used to study current conditions, predict future changes, and reconstruct the past. For example, scientists can input past concentrations of greenhouse gases, which we know from information stored in tiny bubbles in ancient ice, and the model can use that information to simulate past temperatures. Modern climate data and details from natural archives are used to test their accuracy.

Proxy data and climate models have different strengths. The pseudo-statistics are tangible and measurable, and they often have well-understood responses to temperature. However, they are not evenly distributed around the world or over time. This makes it difficult to reconstruct constant temperatures on a global scale. In contrast, climate models are continuous in space and time and, although they are often very efficient, still do not capture every detail of the climate system.

a paleo-temperature puzzle
In our new review paper, we assess climate theory, proxy data and model simulations, focusing on indicators of global temperature. We carefully considered naturally occurring processes that affect climate, including long-term changes in Earth’s orbit around the Sun, greenhouse gas concentrations, volcanic eruptions and the strength of the Sun’s thermal energy.

We also examined important climate feedbacks, such as vegetation and sea ice changes, that may affect global temperatures. For example, there is strong evidence that there was less Arctic sea ice and greater vegetation cover during the period approximately 6,000 years ago than during the 19th century. This darkened the Earth’s surface, allowing it to absorb more heat.

Our two types of evidence give different answers about the trend of Earth’s temperature over the 6,000 years before modern global warming. Natural archives generally show that Earth’s average temperature around 6,000 years ago was about 0.7 Celsius (1.3 Fahrenheit) warmer than in the middle of the 19th century, and then gradually cooled until the Industrial Revolution. We found that most of the evidence points to this result. Meanwhile, climate models generally show a modest warming trend consistent with a gradual increase in carbon dioxide as agriculturally based societies developed over the millennia after the ice sheets retreated in the Northern Hemisphere.

How to improve climate forecasts
Our assessment Highlights: some ways to improve climate forecasts. For example, we found that models would be more powerful if they more fully represented certain climate responses. A climate model experiment that included increased vegetation cover in some regions 6,000 years ago Unlike most other model simulations, which do not include this increased vegetation, we were able to simulate the global temperature extremes seen in the proxy record Were. Understanding and better incorporating these and other feedbacks will be important as scientists continue to improve our ability to predict future changes.

(Ellie Brodman, University of Arizona, and Darrell Kaufman, Northern Arizona University)

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