the cause is understood (orbital forcing), just as today’s cause is understood (CO2 emissions), and these causes are very different.
The reliable instrumental record only goes back 150 years. It is possible to make reconstructions of temperature much further back. These include things like tree rings, ocean sediment, coral growth, layers in stalagmites, and others. The reconstructions available are all slightly different and provide sometimes more and sometimes less global versus regional coverage over the last one or two thousand years. We can reasonably conclude that it is warmer now than any time in at least the last 500 years.
Global warming is not only an output of computer models. It is based on observations of many global indicators. By far the most straightforward evidence is the actual surface temperature record. While there are places that have records going back several centuries, major global temperature analyses can only go back around 150 years due to their requirements for both quantity and distribution of temperature recording stations.
This is actually not an unreasonable point — single years taken by themselves can not establish or refute a trend. A specific year being the hottest globally averaged temperature on record is not convincing.
You can check: The ten-year mean global temperature in 1900 was about 1 degrees Celsius lower than the ten-year mean in 2015.
Every year since 1992 has been warmer than 1992, the ten hottest years on record occurred in the last 15 years, every year since 1976 has been warmer than 1976, the 20 hottest years on record occurred in the last 25
In the 1980s, scientists warn the world of climate change’s threat. Over more than 30 years since, as scientific consensus grew, the research community butted heads with deniers, as companies and industries poured money into denial and disinformation campaigns.
Yet there are still plenty who deny climate change exists, suggesting that snow proves the planet’s not getting warmer, or that climate change is nothing new, so we’ll adapt as we always have. Others claim that volcanoes, or the sun, or heat coming from below the earth’s surface - anything but humans - is responsible.
Exxon’s public position was marked by continued refusal to acknowledge the dangers of climate change, and its continued financial support for climate denial. Over the years, Exxon spent more than $30m on thinktanks and researchers that promoted climate denial. Exxon said that it now acknowledges the risk of climate change and does not fund climate change denial groups. Some climate campaigners have likened the industry to the conduct of the tobacco industry which for decades resisted the evidence that smoking causes cancer.
“There is a lot of psychology involved in this, whether people accept things or not … We’ve been attacked by so-called sceptics about things, who just clearly don’t want to believe, and don’t want to understand the science, who can’t do the maths but aren’t prepared to accept anything we tell them," he says.
against
Climate is complicated and there are lots of competing theories and unsolved mysteries. Until this is all worked out, one can’t claim there is consensus on global warming theory. Until there is, we should not take any action.