Climate change happens slowly over time. The evidence is in the sedimentary rock, in the dried sea beds, in the fossils found in places of very different climate today. Climate change affects all of life, although its impact is measured in geological time. Therefore, although Neanderthals were much affected by climate, separate generations of them may not have realized that a warmer climate was favoring the Cro magnon primates. One might say one reason we know climate change is evident is because we are here.
According to the website arstechnica.com, modern homo sapiens, may have benefited from the long slow melt which led to developments in agriculture as well as advanced tool making. Over the same interlude of warming, the Neanderthals begin to decrease in numbers. The evidence is also found in cave sites, tool artifacts, and encampments.
Although other factors are not dismissed, such as interbreeding, more game, and agile new competitors, it is likely that climate certainly did influence the plants, animals, and therefore humans, at the time of the last ice age, approximately 26,000 to 40,000 years ago. When warming occurred again, it was the less stocky hominids that thrived.
In view of millions of years, there is less fossil evidence, and almost no hominid artifacts except those found in Africa in recent decades. However, researchers again looked at all of the above trends, as indicated by sea beds and recent deserts, sediments, plant life, and core samples, that allow the measure of what life thrived, and what life ceased to thrive, over time.
Other evidence of climate change over time is found in measurable levels of carbon dioxide, changing sea levels, and ever shifting glaciation patterns. In current climate change, for example, scientists look for what is called the increased melting of the perennial ice, as is found in the Greenland ice sheet. They also measure temperatures over time, and it is noted that since 1979 both temperature and carbon dioxide levels have increased considerably. Models are run by computers and can look back millions of years, as well as project predictable patterns of the future.
Climatologists use a great number of metrics and combining them with researchers from fields as diverse as biology and paleo-archeology. They are able to conclude from the vast evidence that climate change over geologic time is more than a popular theory, but a fact supported by a great weight of data. Unfortunately, for current life on earth, the great weight of seven billion people is also being supported by science research as unsustainable. The term for current and very accelerated climate change is described as being created by current use of fossil fuels, and is so called anthropocentric. It is this type of climate change which is charged with heated debate over the viability of so called dirty fuels for human use.