Tim Lenton

Tim Lenton

Professor Tim Lenton is Chair in Climate Change/Earth System Science at the University of Exeter. His research focuses on understanding the behaviour of the Earth as a whole system.

Location University of Exeter

Activity

  • Hi Hedley, I'm pro nuclear power (and pro renewables) myself and not afraid to say so. For me the combination of nuclear electric 'base load' with renewables on top is the way to go for the UK and several other countries. (I am a former student of Jim Lovelock who has always been vociferously pro nuclear.) Admittedly the coverage of future energy options in...

  • Hi Paul, and all,
    The amount of pH change that will happen in the future ocean depends on the amount of CO2 emitted to the atmosphere, which depends on future human activities, so no single value can be given. Rather we can just talk in terms of what ocean pH change corresponds to which emissions scenario. Ceri quotes a range of pH change values that are...

  • Hello Ron and Paul,
    I am happy to see your critical reflection on the content of the course, including this topic of ocean acidification and how it can affect some marine life. You ask about pH measurements - this is in itself a fascinating field - and pH is regularly measured along with the rest of the 'carbonate system', including CO2, in the surface ocean...

  • For what it's worth, I studied Natural Sciences which included mathematics, physics, chemistry (and some other relevant subjects including ecology and history and philosophy of science) (at the University of Cambridge). Peter Cox who did this week's opening video did physics and mathematics and was a nuclear physicist before becoming a climate scientist. But...

  • Yes, Christopher, France's long-term investment in nuclear electricity and a corresponding infrastructure, e.g. the electrified high speed rail network, are a big contributor to their relatively low CO2 emissions. (Vive la France!)

  • Hi Julie, melting ice on land does indeed increase the sea level, as does 'thermal expansion' of the ocean - i.e. heating up the ocean causes the same mass of water to expand in volume. At the moment both effects are contributing significantly to sea level rise. In the future the melting of land ice has the much greater potential to increase sea levels. As for...

  • Hi guys, 1961-1990 is chosen as the reference point because by then we had reasonable global coverage of temperature measurements in order to do an accurate estimate of the global average temperature, which we could reference everything else to. Go further back in time and ship borne thermometer measurements become sparser especially over remote locations,...

  • We'll definitely try to cover the poll results in the feedback video. I really like the suggestion that folk post their justifications for their answers at the end of the week.

  • Hi folks, for more on snowball Earth (from the proponents) take a look at: http://www.snowballearth.org/
    Some of the other lines of evidence include the reappearance of 'banded iron formations' (indicating an anoxic ocean sealed off from the atmosphere by sea ice), glacial striations (scratch marks) in locations with a near-equatorial paleo-latitude at the...

  • I'm liking the flamingo and the reindeer. Looking forward to the next version...

  • Hi all, the Gulf Stream as part of the Atlantic ocean overturning circulation is important in keeping the North East Atlantic region a lot warmer than it otherwise would be. When it comes to the triggering of ice ages in the recent past they are controlled by a mixture of variations in the Earth's orbit affecting how cool the summers are in the high Northern...

  • Love 'em!

  • It gets picked up by the bottom of the glacier by scraping off the soil and sediments underneath, then eventually it gets dropped out of the bottom of the glacier if it flows out over water and the bottom of it melts.

  • Indeed! Happily it is so wet and mild here in southwest England that the barbecue rarely comes out.

  • Hello folks, it's good to see some critical questioning of why Hound Tor settlement was abandoned. Societies and communities are complex systems subject to many drivers, of which climate change can be one, and disease another. It's fair to say that the climate was deteriorating at the location and time when the Hound Tor settlement was abandoned but that...

  • I'm a long-time fan of the Gaia hypothesis - in many ways it is what inspired me to get into scientific research.
    Tim

  • Yes, both long-lived gases like CO2, and short-lived ones like tropospheric ozone (O3) can force climate change. The other thing that defines a forcing is it is something being altered from 'outside' the control of the climate itself, e.g. by volcanic eruptions or human activities. Water vapour is not directly altered by human activities (or at least only by a...

  • Hi Elly,
    Carbon dioxide, nitrous oxide and methane are all long-lived gases (meaning each molecule spends decades to millennia in the atmosphere - a decade for methane, roughly a century for nitrous oxide, and from decades to millennia for carbon dioxide), whereas water vapour is short-lived in the atmosphere (each molecule typically spending days in the...

  • Wow, Vincent. I am wondering if you are the youngest person we've ever had on the course. Do tell your friends about it, and do tell us if we need to make the course easier to understand.
    Tim

  • Just wanted to say awesome job and well done to everyone who has started blogging about the course, and to all of you talking about the course and the content on social media. It cheers me up in these dark political times, and we're getting a great response in terms of more people signing up for the course. So, thank you!
    Tim

  • Hi folks, I guess we will never please all of the people all of the time - but I am glad at least some of you are still enjoying the more societally-oriented content. My personal feeling is that the course is weighted a little too strongly toward the 'challenges' of climate change and not strongly enough toward the 'solutions' - but perhaps some of you will...

  • Hi Carol, your observations about how many trees would be needed to produce as much energy as current coal consumption are very astute - it would require a vast area of managed forests. However, burning wood rather than coal does save a lot on net CO2 emissions because the CO2 you release in burning wood is CO2 that only recently came out of the atmosphere,...

  • Great observations, Alastair - I have written a little about these mechanisms with colleagues but there has been very little fully coupled modelling that properly considers the interaction between ice sheet melt on one pole causing sea level rise that destabilises the ice sheet on the other pole. You are quite right that the Arctic sea-ice can disappear much...

  • That's right, Robert - although the Antarctic sea-ice is not changing a great deal the Antarctic continent is getting warmer and some warm waters have come in contact with part of the ice sheet triggering a potentially irreversible retreat of the grounding line. The question now is how quickly (or slowly) can the ice sheet melt and accelerate sea level rise.

  • Brilliant question, Bill - I'm a specialist on climate 'tipping points' and spend a lot of time trying to work out if one could be close. I agree with you that changing extreme weather is a big deal - and some of it could be linked to the rapid loss of Arctic sea ice. Projecting forward 30 years the Arctic sea-ice could be largely gone in summer and that will...

  • Hi Maaike - excellent observations about the importance of the jet stream. There is a lively debate going on in climate science about whether changes in the jet stream are related to the loss of Arctic sea-ice cover - for example some recent cold winters in the UK (though not the one we just had) linked to unusually southern routing of the jet stream....

  • Hi Peter, and all, the largest fraction of the roughly 5000 GtC of known fossil fuel reserves are in the form of coal. Given the recent rapid increase of coal use in China and India (and therefore globally), sadly I don't think we can rule out the 10-fold increase in coal use in RCP8.5 - there is certainly enough coal available to fuel such an increase this...

  • Hi Bob,
    There is steady heating of the ocean going on all of the time at the moment thanks to the energy imbalance (radiative forcing) caused by human activities. But clearly ENSO variability predates human activities and it is indeed just a redistribution of ocean heat. In essence an El Nino is when the 'warm pool' of water that usually resides in the West...

  • Hi Robert - great comment! Yes, James Lovelock was indeed onto something big with his Gaia hypothesis. In the past the climate was returned to stability by the process of silicate weathering taking up excess CO2 from the atmosphere (helped by biology which accelerates rock weathering). However, that is a relatively slow negative feedback - it takes a million...

  • Hello Bob,

    Thanks for your insightful question. I have never seen the data divided into La Nina, El Nino and neutral periods. What you have rightly identified is that the so called 'pause' or 'slowdown' in global temperature rise was a time when the ocean took up heat even more efficiently than usual, leaving less heat to warm the atmosphere. (As the ocean...

  • The scientists at UEA were shown to be not guilty by several independent enquiries - see for example https://en.wikipedia.org/wiki/Climatic_Research_Unit_email_controversy - it is tragic if this has indeed left a nagging doubt in many people's mind that climate change is not real.

    As to how or why such a controversy blew up it is worth noting that there...

  • Hello Gerald and Ian, the confusion here is that the CDIAC plot you link to of ice core data does not include the present concentrations of the three gases - it just shows their natural pre-industrial variability as trapped in ice bubbles in Antarctica. There is a nice plot from the previous IPCC report which overlays the directly measured gas concentrations...

  • Hi Neil,
    I like the way you are thinking here. It is true that we don't have a complete understanding of the ice age cycles, but we do have models where if we prescribe the changes in the Earth's orbit and/or changes in CO2 (which in reality are generated internally in the system) we can reproduce the pattern of ice age cycles and attribute different...

  • Interesting question! Forest cover will tend to reduce wind speeds for the cities sitting within them, and wind drives both evaporative cooling and 'sensible heat' loss from an area of land surface. Cities in grasslands/deserts will experience faster winds and more effective cooling by these wind-driven mechanisms. Also, grasslands/deserts cool faster at night...

  • Hi Neil, a quick answer would be that yes the Earth's temperature is very sensitive to its overall albedo - known as the 'planetary albedo' - and yes, measuring the albedo from space has got some error bars on it - some of the best data are from 'ERBE' the Earth's radiation budget experiment. If a climate model gets the albedo wrong, for example by getting the...

  • Hi Susan, and all, in the weekly feedback video you'll see an answer to why extreme events can get more frequent in a changed climate, but we don't go into the detail of jet stream meandering, etc, nor the data record of extreme events. There is currently a lively scientific debate about whether Arctic warming and sea ice loss is encouraging larger meanders of...

  • Hi Neil, Liam's asked me to chip in.
    Most of the atmosphere is near the surface (density of the air decreases with height) so the great majority of the blanket is the lower atmosphere or troposphere. If we were able to look at the Earth from space in the infrared wavelenghts then we wouldn't really see the surface, instead we'd be looking mostly at the...

  • Hi folks - the Earth was not completely covered in water 4.2 billion years ago - there were the beginnings of volcanic islands and continent formation. But there was a lot less land than there is today, so weathering was restricted to a smaller area. The continents have grown over Earth history - geologists now have evidence that continent growth happened in a...

  • Hi Tony, the inner Earth was indeed hotter when it was younger - thanks to heat released in the collisions that created the Earth, and the decay of radioactive elements inside the Earth. However, it still had a negligible effect on the overall surface temperature of the planet - except in a few special regions where geothermal heat could reach the surface more...

  • Tim Lenton made a comment

    If anyone is wondering about the dramatic pause in the video, it is where I realise I have just written down 288K (today's surface temperature) when it is actually at 255K that an object gives off roughly 240 W/m2. Hopefully the following bit of the video explains things okay. 255K (-18C) represents the ‘effective temperature’ of our planet, as seen from...

  • I can see the final 'Planck's feedback' is causing some confusion. We will try and tackle it in the weekly feedback video. Before then it might help to think in terms of the energy coming off the Earth being in balance with the energy coming in. Imagine the amount of energy coming into the Earth is fixed - it is determined by the radiation coming in from the...

  • Spot on, Phil - it is indeed the single most important (=strongest) positive feedback in the climate system, and we will return to it later...