Our question this week comes from a father and his two young boys. 
 
They want to know whether it’s possible to plant enough trees to soak up all the extra carbon we are putting into the atmosphere? 
 
The quest to find answers takes us to a remote reforestation project in the Carpathian Mountains in Romania which could be a model for other projects looking to tackle the climate crisis through reforestation. 
 
We speak to experts to find out how much tree planting and reforestation can do in helping combat the climate crisis. 
 
Presenter: Caroline Steel 
Producer: Margaret Sessa-Hawkins 
Editor: Richard Collings

Can planting trees solve the climate crisis?

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Coastlines around the world are changing, causing serious problems for the many communities living near the sea, as well as vital and fragile coastal ecosystems.  In the second of a two-part special on coastal erosion, CrowdScience explores the best ways to tackle this problem. Presenter Caroline Steel visits the Caribbean island of Puerto Rico to see the various methods they use to protect their coasts.  First up: ‘riprap’ – rocks strategically placed to keep the encroaching sea at bay. The problem is, while it protects the area immediately behind the rocks, riprap can exacerbate erosion nearby.   But there are other, more nature-friendly solutions, including sand dune restoration. Caroline picks up her shovel and helps to re-plant dunes, destroyed in the past by erosion as well as sand extraction for the construction trade. The roots of these plants stabilise the dunes, while building boardwalks prevents further damage from humans.   Nature also offers the perfect offshore protection against coastal erosion: coral reefs. These are the first line of defence in absorbing the power of the ocean’s waves. Down on the beach, we see for ourselves just how effective they are. The reefs face threats, but restoration plans are afoot. We visit a nursery that grows corals to plant out on the reefs – and find out about corals’ surprising cannibalistic tendencies in the process.  Featuring: 
Professor Robert Mayer - Director of Vida Marina, Center for Conservation and Ecological Restoration, University of Puerto Rico 
Nada Nigaglioni - Biology student, University of Puerto Rico  
Ernesto Diaz - Caribbean Regional Manager at TetraTech 
Dr Stacey Williams - Executive Director, ISER Caribe  Presenter: Caroline Steel 
Producer: Hannah Fisher 
Editor: Cathy Edwards 
Production Co-ordinator: Liz Tuohy 
Studio Manager: Emma Harth (Photo: Coast restoration measures at Ultimo Trolley Beach, Puerto Rico. Credit: BBC)

How should we protect our coastlines?

Around the world, coastlines are constantly changing due to the power of waves, currents and tides. Coastal areas are also some of the most heavily populated and developed land areas in the world. So it’s not hard to see how the natural process of coastal erosion can cause serious problems for us.    It’s an issue that’s been bothering CrowdScience listener Anne in Miami Beach, Florida. She can see the beach from her window and wonders why after every storm, several trucks arrive to dump more sand on it.   In this first of two programmes, CrowdScience visits Anne’s home in south Florida and finds out how erosion threatens Florida’s famous beaches. Caroline Steel speaks to geoscientist Dr Tiffany Roberts Briggs and hears why it’s such a problem for this tourist-reliant state. Tiffany explains the delicate balance between natural processes and human infrastructure.   Meanwhile, the Caribbean island of Puerto Rico declared a state of emergency in April 2023 due to coastal erosion. Caroline witnesses the impacts of erosion first-hand, as Ruperto Chaparro shows her abandoned houses crumbling into the sea.   But how can we quantify the rate of erosion? Dr Kevian Perez in the Graduate School of Planning at University of Puerto Rico explains the methods they use to monitor Puerto Rico’s coastlines, and how they are evaluating the effectiveness of different mitigation methods.   However, some of the methods used to protect coastal communities from the encroaching sea have done more harm than good. So what are the best ways to tackle this problem? That’s what we’ll be exploring in next week’s programme.   Presenter: Caroline Steel 
Producer: Hannah Fisher 
Editor: Cathy Edwards 
Production Co-ordinator: Liz Tuohy  
Studio Manager: Steve Greenwood and Bob Nettles  Featuring: 
Dr Tiffany Roberts Briggs, Associate Professor at Florida Atlantic University 
Ruperto Chaparro, Director of Sea Grant Programme, University of Puerto Rico 
Anabela Fuentes Garcia, Villa Cristiana community leader 
Dr Kevian Perez, researcher at the Coastal Research and Planning Institute of Puerto Rico at the Graduate School of Planning (Photo: Puerto Rico after Hurricane Maria. Credit: Orlando Sentinel/Getty Images)

Are our coastlines being washed away?

How do we know where a sound is coming from?  Another chance to hear this ear-opening episode, exploring a question from CrowdScience listener Chiletso. One day, he heard his son bounce a ball and instantly knew the direction it was travelling. How?  Anand Jagatia sets out to discover what makes left, right, up and down sound so different.  First, he gets blindfolded, so Alan Archer-Boyd, former auditory scientist and lead engineer at BBC R&D;, can put his sound localisation skills to the test. It turns out that having two ears and pinnae, those flappy bits of cartilage on the side of your head, help a lot.  Professor Eric Knudsen shares how the barn owl’s asymmetrical ears allow it to hunt mice, even in complete darkness.  And Anand uncovers how far he can push his own spatial hearing. Blind activist and researcher Thomas Tajo teaches him how to echolocate like a bat, and Dr Lore Thaler explains what is going on in the brain of experienced echolocators.  This programme was originally broadcast in March 2023.  Presented by Anand Jagatia 
Produced by Florian Bohr for the BBC World Service  Image: Boy with hands at his ears 
Credit: Silke Woweries/Getty Images

How do my ears sense direction?

Today there are over eight billion people on Earth. That’s an awe-inspiring figure… but how does it compare to the vast numbers who came before us? Listener Alpha wants to know how many people have ever existed, so CrowdScience sets out to do a historical headcount. The Population Reference Bureau in the USA estimated this number back in the 90s, and have been updating their calculations ever since. Demographer Toshiko Kaneda explains how their model works, the assumptions it makes – and the huge uncertainties around the number it comes out with. We first need a date for when ‘humans’ first began, so Caroline travels to the Natural History Museum in London to meet human evolution expert Chris Stringer, and marvel at his collection of replica fossil skulls. Chris demonstrates how to distinguish our species, Homo sapiens, from other species like Neanderthals. When did these species first appear - and which of them count as human? And once you know where to start the clock, how do you estimate the numbers of people alive at different points in history? For a population demographer like Walter Scheidel, it helps that some ancient civilisations kept detailed censuses, a few of which have survived to the present day. Caroline and Walter pour over one of these census fragments, and learn how to combine them with other archaeological clues to get some very rough numbers. And finally: what does the future of our population look like? Poonam Muttreja from the Population Foundation of India discusses developments in the world’s most populous country, as well as the big demographic trends ahead for humanity.  Presenter: Caroline Steel 
Producer: Phil Sansom 
Additional Recording: Umaru Fofana 
Editor: Cathy Edwards 
Production Co-ordinator: Connor Morgans 
Studio Manager: Sue Maillot  Featuring:
Toshiko Kaneda, Technical Director of Demographic Research, Population Reference Bureau
Chris Stringer, Research Leader in Human Evolution, Natural History Museum London 
Walter Scheidel, Professor of Classics and History, Stanford University 
Poonam Muttreja, Executive Director, Population Foundation of India

How many people have ever existed?

We spend a lot of our time thinking about climate change, but listener Paul has a question that isn’t usually part of the conversation. He wants to know whether a hotter atmosphere will affect how often volcanoes erupt, or make them more explosive when they do. CrowdScience travels to New Zealand to search for answers, exploring volcanic craters and discovering traditional Maori knowledge about volcanoes. Contributors: 
Geoff Kilgour, Volcanologist, Geological and Nuclear Sciences Taupo, New Zealand
Heather Handley, Volcanologist, University of Twente, The Netherlands 
Pouroto Ngaropo, Historian and Matauranga Māori expert, Rotorua, New Zealand  Presenter: Caroline Steel
Producer: Emily Bird 
Editor: Cathy Edwards
Production Co-Ordinator: Connor Morgans
Sound Engineer: Steve Greenwood (Photo: Icelandic volcano. Credit: KRISTINN MAGNUSSON/Getty Images)

Can planting trees solve the climate crisis?

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