Not getting any response

private let apiKey = "528f441aa2f66ebc1ae1da937070dc40"



override func viewDidLoad() {

    super.viewDidLoad()

    // Do any additional setup after loading the view, typically from a nib.



    let baseURL = NSURL(string:"https://api.forecast.io/forecast/\(apiKey)/")

    let forecastURL = NSURL(string:"37.8267,-122.423", relativeToURL: baseURL)

    let sharedSession = NSURLSession.sharedSession()
    let downloadTask: NSURLSessionDownloadTask = sharedSession.downloadTaskWithURL(forecastURL, completionHandler: { (location: NSURL!, response: NSURLResponse!, error: NSError!) -> Void in
        println(response)
    })


}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}