A former British Petroleum (BP) geologist has warned that the age of cheap oil is long gone, bringing with it the danger of "continuous recession" and increased risk of conflict and hunger.

At a lecture on 'Geohazards' earlier this month as part of the postgraduate Natural Hazards for Insurers course at University College London (UCL), Dr. Richard G. Miller, who worked for BP from 1985 before retiring in 2008, said that official data from the International Energy Agency (IEA), US Energy Information Administration (EIA), International Monetary Fund (IMF), among other sources, showed that conventional oil had most likely peaked around 2008.

Dr. Miller critiqued the official industry line that global reserves will last 53 years at current rates of consumption, pointing out that "peaking is the result of declining production rates, not declining reserves." Despite new discoveries and increasing reliance on unconventional oil and gas, 37 countries are already post-peak, and global oil production is declining at about 4.1% per year, or 3.5 million barrels a day (b/d) per year:

"We need new production equal to a new Saudi Arabia every 3 to 4 years to maintain and grow supply... New discoveries have not matched consumption since 1986. We are drawing down on our reserves, even though reserves are apparently climbing every year. Reserves are growing due to better technology in old fields, raising the amount we can recover – but production is still falling at 4.1% p.a. [per annum]."

Dr. Miller, who prepared annual in-house projections of future oil supply for BP from 2000 to 2007, refers to this as the "ATM problem" – "more money, but still limited daily withdrawals." As a consequence: "Production of conventional liquid oil has been flat since 2008. Growth in liquid supply since then has been largely of natural gas liquids [NGL]- ethane, propane, butane, pentane - and oil-sand bitumen."

Dr. Miller is co-editor of a special edition of the prestigious journal, Philosophical Transactions of the Royal Society A, published this month on the future of oil supply. In an introductory paper co-authored with Dr. Steve R. Sorrel, co-director of the Sussex Energy Group at the University of Sussex in Brighton, they argue that among oil industry experts "there is a growing consensus that the era of cheap oil has passed and that we are entering a new and very different phase." They endorse the conservative conclusions of an extensive earlier study by the government-funded UK Energy Research Centre (UKERC):

"... a sustained decline in global conventional production appears probable before 2030 and there is significant risk of this beginning before 2020... on current evidence the inclusion of tight oil [shale oil] resources appears unlikely to significantly affect this conclusion, partly because the resource base appears relatively modest."

In fact, increasing dependence on shale could worsen decline rates in the long run:

"Greater reliance upon tight oil resources produced using hydraulic fracturing will exacerbate any rising trend in global average decline rates, since these wells have no plateau and decline extremely fast - for example, by 90% or more in the first 5 years."

Tar sands will fare similarly, they conclude, noting that "the Canadian oil sands will deliver only 5 mb per day by 2030, which represents less than 6% of the IEA projection of all-liquids production by that date."

Despite the cautious projection of global peak oil "before 2020", they also point out that:

"Crude oil production grew at approximately 1.5% per year between 1995 and 2005, but then plateaued with more recent increases in liquids supply largely deriving from NGLs, oil sands and tight oil. These trends are expected to continue... Crude oil production is heavily concentrated in a small number of countries and a small number of giant fields, with approximately 100 fields producing one half of global supply, 25 producing one quarter and a single field (Ghawar in Saudi Arabia) producing approximately 7%. Most of these giant fields are relatively old, many are well past their peak of production, most of the rest seem likely to enter decline within the next decade or so and few new giant fields are expected to be found."

"The final peak is going to be decided by the price - how much can we afford to pay?", Dr. Miller told me in an interview about his work. "If we can afford to pay $150 per barrel, we could certainly produce more given a few years of lead time for new developments, but it would break economies again."

Miller argues that for all intents and purposes, peak oil has arrived as conditions are such that despite volatility, prices can never return to pre-2004 levels:

"The oil price has risen almost continuously since 2004 to date, starting at $30. There was a great spike to $150 and then a collapse in 2008/2009, but it has since climbed to $110 and held there. The price rise brought a lot of new exploration and development, but these new fields have not actually increased production by very much, due to the decline of older fields. This is compatible with the idea that we are pretty much at peak today. This recession is what peak feels like."

Although he is dismissive of shale oil and gas' capacity to prevent a peak and subsequent long decline in global oil production, Miller recognises that there is still some leeway that could bring significant, if temporary dividends for US economic growth - though only as "a relatively short-lived phenomenon":

"We're like a cage of lab rats that have eaten all the cornflakes and discovered that you can eat the cardboard packets too. Yes, we can, but... Tight oil may reach 5 or even 6 million b/d in the US, which will hugely help the US economy, along with shale gas. Shale resources, though, are inappropriate for more densely populated countries like the UK, because the industrialisation of the countryside affects far more people (with far less access to alternative natural space), and the economic benefits are spread more thinly across more people. Tight oil production in the US is likely to peak before 2020. There absolutely will not be enough tight oil production to replace the US' current 9 million b/d of imports."

In turn, by prolonging global economic recession, high oil prices may reduce demand. Peak demand in turn may maintain a longer undulating oil production plateau:

"We are probably in peak oil today, or at least in the foot-hills. Production could rise a little for a few years yet, but not sufficiently to bring the price down; alternatively, continuous recession in much of the world may keep demand essentially flat for years at the $110/bbl price we have today. But we can't grow the supply at average past rates of about 1.5% per year at today's prices."

The fundamental dependence of global economic growth on cheap oil supplies suggests that as we continue into the age of expensive oil and gas, without appropriate efforts to mitigate the impacts and transition to a new energy system, the world faces a future of economic and geopolitical turbulence:

"In the US, high oil prices correlate with recessions, although not all recessions correlate with high oil prices. It does not prove causation, but it is highly likely that when the US pays more than 4% of its GDP for oil, or more than 10% of GDP for primary energy, the economy declines as money is sucked into buying fuel instead of other goods and services... A shortage of oil will affect everything in the economy. I expect more famine, more drought, more resource wars and a steady inflation in the energy cost of all commodities."

According to another study in the Royal Society journal special edition by professor David J. Murphy of Northern Illinois University, an expert in the role of energy in economic growth, the energy return on investment (EROI) for global oil and gas production - the amount of energy produced compared to the amount of energy invested to get, deliver and use that energy - is roughly 15 and declining. For the US, EROI of oil and gas production is 11 and declining; and for unconventional oil and biofuels is largely less than 10. The problem is that as EROI decreases, energy prices increase. Thus, Murphy concludes:

"... the minimum oil price needed to increase the oil supply in the near term is at levels consistent with levels that have induced past economic recessions. From these points, I conclude that, as the EROI of the average barrel of oil declines, long-term economic growth will become harder to achieve and come at an increasingly higher financial, energetic and environmental cost."

Current EROI in the US, Miller said, is simply "not enough to support the US infrastructure, even if America was self-sufficient, without raising production even further than current consumption."

In their introduction to their collection of papers in the Royal Society journal, Miller and Sorrell point out that "most authors" in the special edition "accept that conventional oil resources are at an advanced stage of depletion and that liquid fuels will become more expensive and increasingly scarce." The shale revolution can provide only "short-term relief", but is otherwise "unlikely to make a significant difference in the longer term."

They call for a "coordinated response" to this challenge to mitigate the impact, including "far-reaching changes in global transport systems." While "climate-friendly solutions to 'peak oil' are available" they caution, these will be neither "easy" nor "quick", and imply a model of economic development that accepts lower levels of consumption and mobility.

In his interview with me, Richard Miller was particularly critical of the UK government's policies, including abandoning large-scale wind farm projects, the reduction of feed-in tariffs for renewable energy, and support for shale gas. "The government will do anything for the short-term economic bounce," he said, "but the consequence will be that the UK is tied more tightly to an oil-based future, and we will pay dearly for it."

Dr Nafeez Ahmed is executive director of the Institute for Policy Research & Development and author of A User's Guide to the Crisis of Civilisation: And How to Save It among other books. Follow him on Twitter @nafeezahmed