The study of ice cores and tree rings is how, we (modern people) have ascertained that the Earth goes through periods of cooling and warming. Not every cycle mirrors previous ones. To promote man-made global warming is a political ploy. To even think that we, as humans, can have that big of an impact to affect global temperatures is naive. All of this has happened before and all at different rates. Show me the precedence in all the previous cycles that show this warming period is extraordinary. Show me concrete evidence, not theories, that show the current warming period is man-made.
Several reports have been published that contradict the exact reports you have published. Furthermore, the scientific community is rather split on the idea of man-made global warming. I am sure that you only lend credence, and legitimacy to government scientists though...
:hi:
Concrete evidence is available. Where do we need to start? Do you accept carbon dioxide is a greenhouse gas due to it absorbing and re-emitting long wave radiation while being transparent to invisible light? If you do not, you'll need to understand it's chemical structure and bonding, or we can do a demonstration by putting light on CO2 and a control and seeing which heats faster. This was first discovered in in the 19th century so it is pretty well established.
If we both can agree on that, I can point to multiple lines of evidence from there.
The first we will use is ice cores, since you brought it up. We live in an ice age that's been going on for the last 2 million years. People often mistaken a "glacial cycle" of expanding ice fields and glaciers with an "ice age," but any time there is persistent surface ice on Earth it is an ice age, meaning we were not in one from the end of the Cambrian all the way until the Quaternary, or some 300 million years. We live in an interglacial and have for at least 10,000 years, in which all of human civilization has occurred. In this interglacial, like in previous ones, CO2 was at around 250-275 ppm. Until the industrial revolution. For the first time since humans evolved (and in fact in millions of years), CO2 levels are in the 300+ parts per million. In fact, as of this month they are at 400 parts per million. So we can safely say this interglacial is not like all of the others.
Now, we can either a) do the math or b) monitor incoming and outcoming energy via satellite to see the impact that CO2 is having. And we have, CO2 is causing heat to build up within the Earth's systems. This is confirmed via ground weather stations, ocean buoys, and satellite readings, as well as through changes in animal and plant distributions and cycles, not to mention ice volume and cover.
If you are wondering how we know if this carbon dioxide is from us or not, we can either 1) do the math and see how much CO2 should be being produced by the amount of fuels we are burning vs how much is accumulating (it's us) or 2) looking at the carbon isotopes. Now there, are more ways, but these are the two that are the least complex. Two types of carbon isotopes, C13 and C12, exist. The ratio of C13/C12 is low in plants and other terrestrial sources whose molecules mostly have C12. It is very high in fossil fuels. Sure enough, the ratio of C13/C12 is increasing, meaning we have isotopic evidence that it is indeed from the burning of fossil fuels.
To think humans can't impact their environment is naive and ignores all of human existence. We build gardens and plant crops in deserts. We literally move mountains of Earth. We make innovate new molecules and materials. We dig canals. We domesticate and create new crops and animals. We change the weather via cloud seeding and urban heat islands. It is far more arrogant to think we don't impact the climate system, and is akin to the 17th and and 18th century belief that causing an animal to go extinct is impossible.