The concentration of greenhouse gases in the atmosphere hit a record high in 2018 and will lead to more extreme weather, the World Meteorological Organisation (WMO) has said.The UN agency's Greenhouse Gas Bulletin is one of a series of studies to be published ahead of a UN climate change summit being held in Madrid next week, and is expected to guide discussions there.It measures the atmospheric concentration of the gases responsible for global warming, rather than emissions.WMO secretary-general Petteri Taalas said: "There is no sign of a slowdown, let alone a decline, in greenhouse gases' concentration in the atmosphere - despite all the commitments under the Paris Agreement on Climate Change."A summary of the report said: "This continuing long-term trend means that future generations will be confronted with increasingly severe impacts of climate change, including rising temperatures, more extreme weather, water stress, sea level rise and disruption to marine and land ecosystems."The concentration of carbon dioxide, a product of burning fossil fuels that is the biggest contributor to global warming, surged from 405.5 parts per million in 2017 to 407.8 ppm in 2018.This exceeded the average annual increase of 2.06 ppm between 2005 and 2015, the WMO report said.Irrespective of future policy, carbon dioxide stays in the atmosphere for centuries, locking in warming trends.Mr Taalas said: "It is worth recalling that the last time the Earth experienced a comparable concentration of CO2 was three to five million years ago."The annual increase in methane, a greenhouse gas that is more potent than CO2 but dissipates faster, was the highest since 1998, according to the report.The study includes data from dozens of sites as well as naval and aerial measurements.For nitrous oxide, which helps to erode the atmosphere's ozone layer and expose humans to harmful ultraviolet rays, it was the biggest increase ever recorded.Govts asked: 'Where is your climate plan?'Mr Taalas said there were some grounds for optimism ahead of the Madrid talks that start on 2 December.He said: "What is good news is the visibility of these issues is higher than ever."So, personally, I'm more hopeful than I used to be 10 years ago, but of course we have to speed up the process."The UN Environment Programme's (UNEP) annual "emissions gap" report, due on Tuesday, assesses whether countries' emissions reduction policies are enough to meet agreed targets of limiting global warming to 1.5C to 2C (2.7F to 3.6F).A report co-authored by UNEP showed last week that major fossil fuel producers are set to bust global environmental goals with their coal, oil and gas extraction in the next decade.A majority of European Union lawmakers were hoping to symbolically declare a "climate emergency" during a debate on the Madrid conference on Monday, to increase pressure on the incoming EU executive to take a stronger leading role in the fight against climate change.