The human cost of Syria’s civil war, now in its third year, continues to rise. According to the U.N., Syria now has the world’s largest humanitarian crisis.

The U.N. estimates that the number of Syrian refugees, now over two million, will swell to four million by the end of 2014. Nearly half of Syrian refugees are children, leading to concern over Syria's “lost generation.” Within Syria, the numbers of displaced are skyrocketing. More than 6.5 million people are internally displaced, and most of them are beyond the reach of humanitarian aid.

The neighboring countries of Lebanon, Turkey, Jordan, and Egypt are hosting the majority of Syrian refugees. Lebanon has the largest number of refugees, estimated at one million. Nearly one in five people in Lebanon is a Syrian refugee, and the country is facing a crisis. The influx of refugees has taxed Lebanon's infrastructure, schools, and public utilities. With rents skyrocketing and housing becoming unavailable, many Syrians have had to erect tents in the Bekka Valley along the Syrian border or find shelter in abandoned buildings or under bridges in larger cities.

Because of Lebanon’s complex history with Palestinian refugees, who have lived in camps around the country for decades, the government has not allowed the U.N.H.C.R. to provide tents to Syrian refugees—anything that could become a permanent structure. Only recently, after a protracted lobbying effort, did the Lebanese government agree to a trial run of temporary shelters built by the U.N.H.C.R. in conjunction with the Ikea Foundation.

The Syrian refugee crisis is expanding beyond the Middle East into Europe as Syrians flee countries stretched beyond their capacity to host them. Hundreds of Syrian refugees have drowned in the Mediterranean as they tried to reach Europe by boat. Though the journey is dangerous, most of those attempting it feel they have no choice. But Europe is facing a fiscal crisis and austerity measures, and many countries are closing their doors. The U.S. has accepted fewer than 100 Syrian refugees since the civil war began.

The U.N. has just launched its largest-ever single appeal, for $6.5 billion in aid for 2014. However, last year’s much smaller request for aid was only 60 percent funded. With no end in sight for the war in Syria, the prospects for Syrian refugees, including those in Lebanon, grow dimmer.