Evidence of Anthropogenic Global Warming
Similar to the attempts to counter science on the poisoning effects of lead-based fuel or the health risks of using tobacco products, we have serious forces trying to keep the science of AGW at the 'debate' level. The idea is to confuse the public with official sounding counter-arguments so that the scientific evidence is interpreted as 'inconclusive'.
Critical thinkers resolve dilemmas such as this by bypassing the superficial debate and looking at the evidence.
Is Our Planet Warming?
First let's see if global warming is a valid claim - setting aside the anthropogenic (human) element for a moment. NASA (see seed URL) has a perspicuous visual timeline that allows us to see the warming and cooling across the planet from 1884 to 2017. Click on the image below to play with the dials and see the worldwide temperature dynamics for yourself.
The above dynamic is also reflected in a conventional chart:
(All of this data can be downloaded from the webpage.)
Our climate is definitely trending warmer.
Why is Earth Heating Up?
Carbon dioxide (CO2) is an important heat-trapping (greenhouse) gas, which is released through human activities such as deforestation and burning fossil fuels, as well as natural processes such as respiration and volcanic eruptions.
Worldwide CO2 levels over time is available to visibly see what is happening. Click on the image below to investigate this:
And a conventional chart reflecting the CO2 parts per million since 2006:
And scaling back to see the trend over the past 400 thousand years reconstructed from ice cores.:
The Earth's climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives. The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20thcentury and proceeding at a rate that is unprecedented over decades to millennia.1
The planet is heating up and CO2 levels in the atmosphere is the primary reason. This is the greenhouse effect:
Most climate scientists agree the main cause of the current global warming trend is human expansion of the "greenhouse effect"1— warming that results when the atmosphere traps heat radiating from Earth toward space.
There are several greenhouse gases involved, but CO2 is the main player.
Carbon dioxide (CO2). A minor but very important component of the atmosphere, carbon dioxide is released through natural processes such as respiration and volcano eruptions and through human activities such as deforestation, land use changes, and burning fossil fuels. Humans have increased atmospheric CO2 concentration by more than a third since the Industrial Revolution began. This is the most important long-lived "forcing" of climate change.
Why are CO2 levels so high (and rising)?
Humans are the Most Likely Cause?
On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2). This happens because the coal or oil burning process combines carbon with oxygen in the air to make CO2. To a lesser extent, the clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.
In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change, a group of 1,300 independent scientific experts from countries all over the world under the auspices of the United Nations, concluded there's a more than 95 percent probability that human activities over the past 50 years have warmed our planet.The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels from 280 parts per million to 400 parts per million in the last 150 years. The panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in Earth's temperatures over the past 50 years.
The Intergovernmental Panel on Climate Change full report: Summary for Policymakers
A Summary-level Source
The following video offers an easily followed discussion of Global Warming and the likelihood of AGW:
It would seem the trend is clear. The planet is warming and human behavior is a significant contributor.
We all have heard doomsday prophecies from those who have a political (or financial) agenda to 'push' AGW (for example, Al Gore) and of course the exaggerated projections now come back to discredit the science (even though it was talking heads who pushed this). Recent studies show that the AGW is bad but not 'Al Gore' level bad. Let's disregard the hype and not let it discredit good science.
The real questions deal with projecting when the damage will be too great to reverse and what measures we can realistically take to reduce our negative effect on the planet. There are a lot of unanswered questions, but AGW is certainly real and is an existential threat.