Some misguided people, today, who may call themselves "pronatalist", and who look at future predictions of negative population growth (meaning that population will decrease in the future, instead of continuing to increase), and see this as a problem, are wrong or are not thinking clearly. Some of them may believe that African and Arab and Asian populations are in the process of "replacing" or at least are overtaking the Caucasian, European-based ethnicities that have traditionally been the majority of the population in countries like the US, the UK, Europe, Canada, Australia and New Zealand; and they are right - this is indeed happening, as is the Hispanicization of the US population because of such massive immigration. And they are right to be concerned about this. In a century there may be no nations left on Earth where Caucasians of European ancestry are the majority of the population if immigration is not stopped. And this is a problem. There will be African majority countries, Asian majority countries, Arab majority countries, Hispanic majority countries, but there will not be any Caucasian of European ancestry majority countries left if we do not take action now.

Scientists and politicians say we are facing a planetary crisis because of climate change.

But what's the evidence for global warming and how do we know it's being caused by humans?

How do we know the world is getting warmer?

Our planet has been warming rapidly since the dawn of the Industrial Revolution.

The average temperature at the Earth's surface has risen about 1.1C since 1850. Furthermore, each of the last four decades has been warmer than any that preceded it, since the middle of the 19th Century.

Emissions of CO2 driving rapid oceanic acidification

The world's oceans are becoming acidic at an "unprecedented rate", more rapidly than at any time in the past 300 million years. In their strongest statement yet on this issue, scientists say acidification could increase by 170% by 2100. They say that some 30% of ocean species are unlikely to survive in these conditions. The researchers conclude that human emissions of CO2 are clearly to blame. The study will be presented at global climate talks in Poland next week.

In 2012, over 500 of the world's leading experts on ocean acidification gathered in California. Led by the International Biosphere-Geosphere Programme, a review of the state of the science has now been published. This Summary for Policymakers states with "very high confidence" that increasing acidification is caused by human activities which are adding 24 million tonnes of CO2 to oceans every day.