At the age of 91, Sir David Attenborough lay down in the sand next to a giant nesting leatherback turtle — and his face says literally everything you need to know about how he feels about ocean conservation.

The expression in the veteran broadcaster’s eyes is half respect for the turtle’s majesty, and half disappointment that humanity has so spectacularly failed to protect the oceans and marine life. 

His latest series, "Blue Planet II," has proved a vital tool in bringing plastic pollution and the damage it’s doing to the seas into the public domain. 

Take action: Fight Waste to Protect Our Oceans

“The oceans are under threat now as never before in human history,” he said, in Sunday night’s series finale. 

And, my word, that message really hit home, with Twitter users turning out to express their dismay at letting down this most beloved national treasure.

The "Blue Planet II" series has focused on the changing nature of seas and oceans, and the impact that humans are having, including through plastic pollution, overfishing, hunting, and damaging tourist practices. 

But, despite some of the episode’s desperate imagery of animals suffering because of the damage humans are doing to the planet — such as the albatross chicks being fed plastic by their parents — the series ended on a message of hope. 

Read more: 'Shocking' Rise of Litter on Britain's Beaches — and 20% Is From 'On-the-Go' Food and Drink

The episode told stories of conservation successes and its heroes, as Atternborough nudged us towards turning our feelings of guilt into action. 

Viewers saw how overfished herring stocks and orca numbers have recovered off Norway, thanks to timely intervention; how giant leatherback turtles were saved from extinction in Trinidad thanks to education and careful management of tourism; and how whale populations have increased around the world since a hunting ban was introduced in the 1980s. 

“We are at a unique stage in our history,” said Attenborough, in his summing up. “Never before have we had such an awareness of what we are doing to the planet, and never before have we had the power to do something about it.” 

Read more: Sir David Attenborough's 'Blue Planet II' Team Pick Up Every Bit of Litter They Find in the Ocean

“Surely, we have a responsibility to care for our blue planet?” he added. “The future of humanity, and indeed all life on Earth, now depends on us.” 

And, if the Twitter reaction is anything to go by, Attenborough's gentle words could be a powerful rallying call for change. 

An estimated 8 million tonnes of plastic end up in the ocean every year, and by 2050, it is predicted that there will be more plastic in the sea than fish. 

Read more: How China's Shock Decision to Ban Recycled Plastic Is an 'Impending Crisis' for the UK

In the UK, the amount of litter washing up on beaches has risen by 10% in the past year alone, according to the Marine Conservation Society (MCS).

At the MCS’ annual beach clean, which monitors the amount of rubbish on 340 British beaches, some 20% of the litter found was from “on-the-go” food and drink packaging, including cups, cutlery, plastic bottles, coffee stirrers, and sandwich packets. 

Global Citizen campaigns to achieve the Global Goals, including the goal to improve life below water. You can join us by taking action here


Defend the Planet

Viewers React to Finale of David Attenborough's 'Blue Planet II'

By Imogen Calderwood